They have dozens of models on their site - which 3 in particular were you looking at?
There is only one aspect ratio you should consider: 16:9 - Most of their 4:3 ratios are for smaller or older TVs. Time to move up to HD, and for HD you need 16:9.
Of the ones on the page you linked to, the 37" models. You will see that some have an over-the-air built in HD tuner (you need an antenna for that!). Some have speakers on the bottom, others on the side, some have a PC card slot, etc. The glass is the same on all of them, but the features inside the case are slightly different. All should perform the same if you are feeding the set HD cable or something like that.