I just saw that season 28 (28????) started. Thinking back, I only watched a few seasons:
I only caught the finale of TUF 1, seeing the amazing
TUF 2 was the first season that I watched most of. I became a huge Rashad fan cause of his performance
TUF Hughes vs. Serra (I wasn't super interested, but I was home at the right time to catch it when it was one)
TUF Rampage vs. Evans (cause it was an awesome rivalry and Kimbo/Roy Nelson on the show really helped)
That's it for me though. I never really watched any seasons after that.