Which laptop printer should I buy?
I can't really recommend one before I fully understand your needs or you fully understand your own needs. There are many different kinds to choose from, the first and most important thing to know is the amount of money you have to spend on it. Once you've concluded that it's enough to buy a laptop printer, you have to decide if you need color printing or you are fine with monochrome only output as well. Are you going to carry it around daily or put it on the back seat of your car. If you've got everything decided and settled you are good to go hunting. In this article I collected three of the better portable printers, all of them are different in some way but you would make a great deal with either of them.
Pentax Pocketjet 3 plus
In spite of the name this printer is not using cartridges to produce the output, it uses thermal printing instead. Thermal printing requires special paper to be bought, think fax machines. It heats the paper where the text should be and this heat sensitive paper turns black where it's put under treatment. I'm stating the obvious here, but do not let direct sunlight or excess heat to get in contact with your prints or they can deteriorate or lose information faster than they would normally. The printer can run on an AC adapter Pentax includes, or the built in battery the company also includes in the default pack. With the battery installed the whole unit weighs just under one pound so putting it in your backpack therefore it won't be a bigger inconvenience to carry around than an umbrella or a lunchbox.
Printing capacity is 4 pages per minute but you can achieve faster operation than that, the manufacturer was a little conservative on its estimate. For $300 this unit is slightly expensive but I don't see how you could get a better pocket printer this small for this amount of money.
Canon Pixma iP100
Canon has been an industry leader in laptop printers and they've done everything to earn this reputation. With their Pixma iP100 model they've proven that they deserve to be on top for just a little more. The iP100 features everything a small printer this size can, including A4 printing in both Color and Black and White modes on virtually any media. It prints normal 80gr paper or the better quality 100gr, labels, business cards envelopes and photo paper are no obstacle.
For a portable printer it provides a remarkable printing experience with 4" x 6" borderless photo printed in 50 seconds, or 20 monochrome pages in a minute. In color mode it gets 14 done in the same time. With the optional lithium-ion battery this printer can be had for $200 but it is expected to drop a little with announcement of new models. It is a decent printer for its price and its 4.5 pounds weight is not going to be a big commitment to carry around on daily basis either.
HP Officejet H470b
The officejet is also powered by an internal battery and claims to print 22 pages a minute or 18 in color. My experience is that these numbers are usually a bit optimistic guesses on what users use the printer for so I'd go with a safe 15 in monochrome and 10 in color estimate. It doesn't weigh too much either, with 4.6 lbs it is only slightly more bulk than the canon model. It also prints on almost anything you can think of as long as it is smaller than A4. For $250 it is a decent choice and I don't know of a reason why you shouldn't decide to get one, if you need a good laptop printer of course.
Some great printers are on the market, some are cheap some are not quite, but you can always find one that meets your needs. Before spending some hard earned money on one of them I'd suggest you check out some other reviews, forum threads or articles about the one you fancy, and buy one when you're sure you've decided well.
Which laptop printer should I buy?