Honestly this decision is most without a doubt up to the gardener. Many gardeners like a variety in their flower garden. Planting both will give you endless possibilities. Some may design their landscape beds by putting tall perennials in the back of the design such as shrubs. There are at least 64 different kinds of perennial shrubs. Arborvitae, Barberry, and Boxwoods are some of the few used more commonly. Using evergreen shrubs can grant your scenery year round essence and color.
Next, you may want to use smaller, but similar plants. Lets say you use Asiatic Lillie's and maybe some Tulips. This could really spice things up. You will achieve astonishing color and an exquisite landscape. Now don't forget that the tulips are basically annuals. They will need to be replaced next year. Fear not, this is an easy task. Once these tulips are done for the season and die, dig up the plant and keep the bulb. If stored properly, you will be able to replant this bulb. However, you must make sure you plant it before the first hard frost. If you want those beautiful flowers to pop up and start flowering in about April through May, you will need to plant the bulbs in early September through December. Deciding when to plant will really depend on what type of winter climate you have and when you get generally get your first hard frost of the year. You should also take the bulb and separate it like you would cloves of garlic, throw out the little bulbs and save the bigger ones for replanting. These bulbs will have a higher survival rate.
Okay, now comes the easy part. It's time to plant the front of your landscape. In my past planting experiences I haven't really had to choose if it was annual or perennial I was planting. I just made sure that the plant looked good in front of my landscape. Of course that is my opinion. I would say look at your color scheme and choose your plants this way. Look to see if it is a perennial or an annual to make sure it can survive it's planting location. Many annuals will flower long periods of time if you "dead-head" the spent flowers. Or if you want to use a ground cover that is abundant in color, I would recommend "Creeping Phlox", or "Wave Petunia's". Creeping Phlox comes in beautiful hues, of purples and pinks both dark and light. Wave Petunia's are almost virtually maintenance-free. They bloom in waves and also come in practically the same colors as Creeping Phlox, the difference is that "Wave Petunia's" generally don't need deadheading and can be used in either hanging pots or for ground cover. There are never-ending ideas when it comes to planting flowers in your landscape, all you have to do is keep trying until you find an idea you like and are satisfied with.
Photo curtesies go to http://www.fotopedia.com/items/flickr-2463206337 and http://www.flickr.com/photos/19966030@NOO/524999359