I was able to try out several different types of snow shoes last winter at a demo weekend at one of the ski areas in Waterville Valley, NH. I think they run them all over the country a couple weekends each winter. I'll try to post something when I get a schedule for this winter. Places that handle cross country gear will frequently have snow shoes, and let you demo them.

My son and I tried various contemporary models made by Tubbs and LL Bean. I tried one for "walking" and several others that could handle backpacking loads. It's important to try before you buy, since the style of binding, the crampons, frame, and webbing can all vary quite a bit.

If you're backpacking, make sure you have them sized for your weight PLUS what you'll typically be carrying. In winter, we sometimes have heavy packs, with extra clothing, food, heavier sleeping bags, and a 4 season tent.

I think a ballpark sizing guideline is something like;
8x25 120-200lbs
9x30 170-250lbs
10x36 220-300 lbs
That's about what Tubbs seems to recommend. I think Bean's are similar. (The sizes are in inches, a 9x30 frame is 9 inches wide, and 30 inches long. There are different shapes, and even male and female versions of some shoes, since I guess our strides are a little different.)

For me, around 190lbs, the 9x30's are great for walking, with just a daypack or butt pack. If I carry a 40-50lb pack, however, I'm still in the 30 range, but, at the high end of it, so in powder, I'm going to be wishing I had the additional "loft" of the 36's. They are a lot more to drag around though. In packed or icy conditions, the more important thing might be how aggressive the crampons are, so you really need to know what you want to do. That's why a couple demo hikes are important, I think.

(Don't ask why I have 50 lbs of stuff, I just seem to carry heavy in winter. Summer I wouldn't want more than 35lbs.)

Somebody else mentioned boots. They are going to be important too, I tend to wear pac boots, like my Sorel's with the snow shoes, but, you need to make sure the bindings will be able to get a good fit on your particular boots of choice.