Re: tractor seat or round
I had a shitty round Mapex throne that actually snapped in half (I'm not a big guy at all either) and recently went through the round vs. tractor decision process. I should have taken pictures of it but didn't think to. Was kind of hilarious as it happened while I was practicing and I fell off, very nearly having my anus impaled by the metal rod that had snapped.
Anyway, I'm average height and pretty light weight and found that the tractor style definitely suited me more. Round felt constrictive and didn't contour to me the way the tractor style did. I sat on a fancy looking round Pork Pie at Guitar Center but it was extremely uncomfortable and I felt like I was off balance the entire time sitting on it. Could have been defective though. To be fair, the entire selection there was pretty poor though.
Felt good about the Tama Ergo Rider but went to West to check out the Roc N Soc that gets so much praise. Was stiff and uncomfortable and the hydraulics didn't do anything for me either so it was a pretty easy call.
Advice: DON'T just buy one online. Get your ass in a store and sit on them. I was ready to buy a Roc N Soc after seeing all the positive reviews but if I had, I surely would have returned it because it wasn't a great seat for me. YMMV.