I'm not sure Lockyer would go down as the best player in either of his positions from the 20 odd years I have watched the game.
At fullback he's very close. Slater from about 06-14 though was pretty sensational. Minichiello's years pre back injury were absolutely elite, longevity hurts him. I was a massive fan of Tim Brasher back in the day also, mostly from his NSW performances, but he probably wasn't quite Lockyer's standard. edit - Jarryd Hayne as well, obviously. Probably the most brilliant but not the most consistent (has played with some spuds, of course).
There's been a huge amount of good fullbacks, it's probably been the strongest position of the past 15 years.
At 5/8 I'd prefer Fittler to Lockyer. Great player.
Would've loved to have seen Lockyers career had he remained at fullback, but moving probably added a few years to his career - few less miles in the legs in the front line compared to fullback
Thurston has been the best half of probably the last five years since Lockyers retirement, and probably was before that.
I think Lockyers consistency may be over stated. Pretty regularly over his last few years he looked finished early season, took a while to get going particularly post knee injury. He'd usually come good around round 7-8 in that time.
Lockyer's performances in green and gold were generally really strong, Thurston in Origin has been the biggest difference though across the last 11 years or so, he's a wonderful player in that very good qld side.
Lockyer was great in clutch moments, probably a cooler head than Thurston.
I think Thurston took longer to really mature into his best, he's calmed down and been a much better leader the last 3-4 years. Before that he was obviously high quality but not always a great head, especially at club level. Admittedly he had some mediocre supporting casts, but I wouldn't say he's ever had an amazing three quarter line at club level, but he's getting more out of them now. His forward packs great improvement in recent years has been pretty key to the Cowboys improvement.
Not sure defence is really a difference maker between these two at all. Thurstons defence was mediocre for a long time and even now he's got misses in him. Might hit a little harder than Lockyer ever did. It's a point of difference between both of them and Johns though, who really was a high class defender.
I would have Thurston, just. I love his involvement. Moments like that stretch against the broncos a few weeks back, when he was in absolutely everything in that comeback. He's a brilliant competitor and, with the aforementioned maturity, it makes a pretty brilliant footballer. It really is splitting hairs between the two though. Both extremely good players.