I use Alias WaveFront because I can use it at work and I have learned it several years ago. It is kind of heavy software for just simple polygon models though. It is used e.g. in car design.
If you are new to 3D modelling, I recommend using a program that feels easiest and meets your requirements. Ac3d is not a bad choice and it is not too expensive either.
...off to bed now, already past midnight