Some seasons of TUF are obviously more impactful than others, but there have only been a few seasons where we only see 1 or 2 decent fighters. Say what you will, but TUF does produce solid talent. The first season of TUF was obviously the make it or break it deal, and I'd say it hit a grand slam.
I noticed(long ago) that MMA fans are some of the most hypocritical assessors of any sport. It's quite amusing to hear statements made like,
"these TUF guys never pan out. you get one decent fighter for every few seasons it seems."
Here are best fighters that came from each season.
TUF 1: Forrest Griffin, Stephan Bonnar, Josh Koscheck, Diego Sanchez, Kenny Florian, Chris Leben, Mike Swick, Nate Quarry
TUF 2: Rashad Evans, Joe Stevenson, Josh Burkman, Marcus Davis, Melvin Guillard, Kieth Jardine
TUF 3: Matt Hamill, Michael Bisping, Ed Herman
TUF 4: Matt Serra, Chris Lytle, Patrick Cote, Travis Lutter, Jorge Rivera, Pete Sell, Din Thomas
TUF 5: Gray Maynard, Nate Diaz, Joe Lauzon, Matt Wiman, Cole Miller, Manny Gamburyan
TUF 6: George Sotiropoulos, Mac Danzig
TUF 7: Matt Brown, Amir Sadollah, Matthew Riddle
TUF 8: Ryan Bader, Tom Lawlor, Krysztof Soszynski, Vinny Magalhaes, George Roop
TUF 9: Ross Pearson, DeMarques Johnson
TUF 10: Roy Nelson, Matt Mitrione, Brendan Schaub
TUF 11: Seth Baczynski, Chris Camozzi, Court McGee, Nick Ring, Brad Tavares
TUF 12: Michael Johnson, Nam Phan, Jonathan Brookins
TUF 13: Tony Ferguson, Ramsey Nijem
TUF 14: Diego Brandão, T.J. Dillashaw, John Dodson, Steven Siler, Johnny Bedford, Dennis Bermudez, Akira Corassani, Marcus Brimage, Louis Gaudinot
TUF 15: James Vick, Michael Chiesa, Andy Ogle
TUF 16: Colton Smith, Mike Ricci
TUF 17: Kelvin Gastelum, Uriah Hall, Josh Samman