The trend seems to be shifting towards the iPod Touch, although I always preferred the original iPod ("Classic" now), since I value storage capacity over functionality, and I have an Android phone should I ever want to browse or have fun with useless apps. The three models appeal to different kinds of people though:
As mentioned above, if you have a generous music/video collection or if you enjoy lossless formats, then the Classic's probably for you. I think this generation offers 160gb of storage for about $299, though I can't confirm. I'm still using my 80gb from the 2006/2007 model year.
The iPod Touch is the most versatile of the three in the sense that its functionality goes far beyond playing music/video or displaying pictures. You probably know all about the different apps available, and while many of them are indeed useless, some might end up pretty useful.
The iPod Nano is for you if you have a modest music collection, and that's all you're looking for. It has photo and video-playing capabilities but imo the screen is still too small to watch a full movie on. On the plus side, it's the most affordable option as well as conveniently lightweight.