I am adding 3D models to a game engine I am building, and wanted some opinions on which file format(s) to support. There is a lot of info available on .3ds, .obj, .md2 and .md3, as well as tutorials on how to load and use the models. What are the pros and cons of these file formats?

md2 and md3 are both good and easy to load file formats with animation, im not certain but i dont think obj files have animation.

.x is also a model format, if you want to use directx. The only one I have come in cntact with earlier is .3ds. It worked ok for our purposes, to make a 3D game for school. But I can''t really give you any comparison between the others you mention.

md2 is the easiest to load. md3 is the advanced version of it.
if you dont want a very complex engine, use md2. if you want dynamic lightning and other fancy stuff, use md3. guess with the hardware of today you would go for md3.

.lick