Sorry, of course I messed up - meant "library" where "engine" stood. Edited just now.
Thank you for your post. I guess I wouldn't mind the API changing since the prof clearly stated he isn't interested in the version we're using as long as it solves the problems he'll throw at us and the projects we'll make to pass the course. Having said that, do you think it'd be more rewarding to go with the newer versions?
Ohh, I misread, I thought it was "freedom as long as you used OGL 2.1 and FreeGLUT"
More rewarding? Well yes. 2.x is old, very old. Newer API calls are different, newer GLSL is different, etc.
You'll understand quite a bit more of how graphics work going the OpenGL 3+ core profile route. Drawing your first perspective projected triangle will be pretty hard, but think that drawing 500 thousand more after that first one will be much easier.
To be fair, your professor might teach a more modern "style" of OpenGL 2.1, with shaders and such, so the differences won't be that great, but he might teach the "fixed function pipeline", and in that case the differences will be pretty big.