Tom is right about the Tube Frame vs. Large frames for 'heavier' work', but the higher Hp. tube frames like the H14 and H16 are danged capable as well.
You wouldn't go wrong with the Case, Ingersoll tractors either. It's just seems that the Bolens are a lot easier to find.
MTF is a pretty decent forum, and I'm a member there, but I find that the GTTalk forums are a lot more active, and have some really good, friendly folks with a lot of GT knowledge.
Here's a link to the Bolens sub-forum:http://gardentractortalk.com/forums/forum/4-bolens/
They also have sub-forums for most of the other older GTs as well.