It totally depends on the plants.
Basically there are a couple different strategies for making your garden look nice year-round. They are not mutually exclusive on a "per property" basis, but any given bed will tend to be one or the other:
-- you can make a whole planting (bed) to peak in a particular season, and just don't look too hard at it the rest of the time. This works better with larger properties than with postage-stamps, but even in a small plot you can usually (if you want) have some bed somewhere that is stuffed full o flowers for one season and hidden behind a conveniently-located barbecue (or whatever) the rest of the time
can be done with annuals, bulbs, perennials, or a mix thereof.
-- you can use primarily long-blooming annuals in a bed, so that the whole bed is in flower most of the growing season. Then don't look at it in wintertime
-- you can use mainly a variety of well-chosen perennials, or perhaps perennials and some well-behaved tolerant shrubs, to devise a bed that always has some reasonable amount of stuff in bloom. Annuals can sometimes be popped in the ground, or containers set in gaps, to help pump up the display during thin parts of summer if you are especially ambitious. This approach is hard enough to do well for a very large bed, and not usually terribly successful for a small bed unless you are happy-enough with a relatively low ratio of flowers to foliage. Because, realistically there just WILL be a bunch of things at any given point of time that are not blooming. You can select them as best possible to have attractive foliage and seedpods and all that, and good wintertime form (shrubs are especially useful there), but a blooming-all-year bed is just never going to be the same blaze of color than a meant-to-peak-at-one-particular-time bed will achieve.
If you want spring + summer stuff, one approach that is often useful (except in very hot places) is to plan a summer bed with long-blooming perennials that are planted with just sufficient spaces between them to tuck in clumps of spring-blooming bulbs; and then once the bulb foliage is basically kaput in mid-summer you can stick pots of annuals on top of those spaces for further color (tho you will have to water those containers quite frequently).
As far as exactly what plants give best or longest bloom, it depends hugely on your location and soil.
IMHO a good way to get started with perennials is to read a couple books so you know what the fairly easy ones are that're well-suited to your zone, soil and sun exposure, and then just buy a random sampling of those spp, whatever catches your eye, stick 'em in the ground any ol whichway and get to know them for a year or two. If after that you want to move some (or even get rid of some, or if they get rid of themselves <g>) it is easy enough, but you may well find that you can build the design of the bed around those initially-randomly-placed plants and still end up with a good looking arrangement
(e.t.a. - and learn which plants that do well in your zone have 3- or 4-season interest. For instance, up here, probably the best fallback to stuff into any ol' sunny not-too-wet spot and have it look really good 12 montsh of the year is Autumn Joy sedum or similar cultivars - lovely green mounded foliage emerging fairly early in spring, flowers in early/mid-summer going from whitish to pink to red, the red flowers remaining in autumn with the foliage yellowing handsomely, then the brown remains of flowers standing attractively through nearly all the winter's snow and ice before I yank 'em out in the spring when the new growth starts. It is not an exciting plant but when you have to look at a spot 365 days a year it starts to have a lot to recommend it <g>)
Good luck, have fun,
Pat
