Making passive income through the many online writing sites out there is becoming increasingly popular, and there are new sites popping up all the time. Knowing which are easier to use and will earn you more than others isn't always easy to tell however. Fortunately I have tried nearly all of them, and there are several which stand above the rest.
This site is ideal for beginners purely for the fact that the titles of the articles are already set out and all you need to do is write them. Your articles are then ranked against all the other articles under the same titles using their user rating system. This can be a bit hit or miss however, as the rating is done by other members of the site, meaning it isn't always accurate and for certain topics can tend to be based on personal opinion rather than the article content.

The earnings on helium are generally good, although like a lot of sites they are secretive about what their cut of the advertising revenue is. From the way the earnings work, it seems as if you get around 50% of the ad revenue from impressions, although clicks aren't paid, so you won't see your article earnings suddenly jump up.

Writers there are ranked by how many stars they have, which they can gain for writing and rating. The stars run from 0-5, and are given for having an average article percentage score above a certain figure. Rating stars are done purely on the amount and quality of rates you have done recently. Probably the best thing about Helium however that other sites don't have is that it updates every couple of seconds, so earnings update almost in real time. Most sites will only update once per day or even less.

There are also other features of helium which make it a good site for beginners, including a helpful community, mentoring for new writers and also a marketplace for more experienced writers who can sell articles for a fee. There are also competitions and often different schemes run on the site to increase earnings, such as currently all members who have stars are paid for each article they publish. Helium is also available internationally, which means that if you can open a Paypal account, then you can earn from helium. You can also reprint Helium articles on other sites, which is worth noting.
Although this is one of the most popular sites out there, the earnings are actually a lot lower than they are on many other sites. For every 1000 page views a new writer will earn only $1.50, although this does increase slightly the more views you get. The earnings are said to be a lot better for writing original and requested content rather than just reprinting other articles you have already written. The site seems to work along the lines of paying you more up front if you only print the work there and nowhere else.

The site itself is fairly easy to post on, although the rest of the site is difficult to navigate. It isn't always apparent where you should send queries or get help with a particular topic. The owners of the site aren't too visible which is disconcerting, although the site itself is still one of the largest which seems to suggest that a lot of people still like it. You are allowed to publish already published articles on AC, and are able to reprint them from here on other sites also so long as you keep the introduction paragraph the same.
This site is based in Israel, and like helium is internationally available to anyone with a Paypal account. it has only been operating for a few months, and in that time its popularity has skyrocketed. Although you can publish original material there, it seems to be a place where people republish their work from other sites mainly. Whether this is a good idea in general since google tends to take a dim view of duplicate content will have to remain to be seen although articles not doing well on an original site might be worth reprinting.

The earnings  on Bukisa are based per 1000 views similar to AC's, but the rate at which you are paid is the same for everyone, and fluctuates depending on how well the site itself is doing. So far it has been a lot higher than AC in terms of earnings, although they only pay for original views and not just for each view, which probably lowers earning potential a lot.

They also have a network program where every person you invite makes you an extra percentage of what they make. Because of this, mass e-mails were commonplace on a lot of other sites when Bukisa first started, which quickly gave the site a bad name among some writers. The actual site itself is very easy to use however, and publishing is very quick. Even if you don't intend to submit anything new to Bukisa, it is worth submitting older articles there if the sites they are currently on allow it.

This site works a little differently to the others already reviewed in that its writers are paid from people clicking ads rather than sharing page impressions. In practice this means that articles will tend to jump up by 50 cents here and there rather then earn a few cents each day. The actual percentage of clicks that the writer gets is kept a secret by the site, although this isn't anything totally unusual.

The articles on this site also have to be written in a how to format, and as such need to be actionable or instructional. This means that articles which are only informative, no matter how good they might be, are usually removed. This format does make writing the articles fairly quick however, and the steps being broken up seems to help in making the ideas flow.

Although this site is probably the best earning, the writers have to pay attention to SEO and target audiences and so forth a lot more then they do on other sites if they want to earn a lot. The top writers there earn over $1000 per month, although they are generally very experienced and professional writers.

The major problem with this site is that there are a lot of bugs on the site, and it isnt uncommon for drafts to disappear or for earnings not to be updated for days on end. There are also sometimes issues with publishing, and the more inexperience writers there will constantly message you asking you to read their new article which is annoying. (This is also pointless seen as other writers views arent counted in earnings).
This site is the new kid on the block as far as writing sites are concerned and like Bukisa is only a few months old. Unlike Bukisa however, it is being lauded as the next big thing on a lot of blogs and forums where writers tend to gather.

The earnings on infobarrel are all handled by Google rather then being displayed o the site itself, which means that you will need an adsense account to use the site. The share of the ad revenue that the writer gets is also clearly displayed and is an impressive 75%, which is a lot higher than most sites which tend to give between 25% and 50%.

The site itself is easy to use, and utilizes how to formats, reviews, videos and blank articles, meaning that most writing styles are catered for. Writing is also easy to do, and the text editor on the site is a lot better than most of the other sites tools.

There aren't seemingly any problems with the site thus far, although it has only just started, and time will tell what it turns out like. Seemingly at this stage the article categories and sub categories are a little limited, although I imagine these are going to be added to in the near future.

The best approach as with most things in life is to try each one and see what works for you. Personally I started out with Helium, where I currently have nearly 1000 articles. I also have 300 on AC and about 100 on Ehow and another 100 on Bukisa. Infobarrel is my latest experiment, and I have only posted a couple of articles there so far.

From Helium I branched out onto the other sites, and the earnings seem to be the best either there or on Ehow at the moment. Remember to check the terms and conditions of the sites you write on, and if they allow it you can reprint articles on other sites which accept reprints.

Certain sites are also better for certain types of articles than others, for example AC will tend to earn you at least something for every article you could think to write on there. The best earning articles there tend to be those which are interesting to casual readers rather then informative or high earning in terms of ads. Helium by contrast will usually earn nothing for an unpopular article such as creative writing or poetry, and a lot more for articles with high ad revenue such as medical articles.