I have them all and the one that I fly the most would be the Trex 500 its more stable in the wind and I like the size in the air easer to look at too. My least favorite bird and the biggest disappointment would be the Trex 250.
The Trex 600 and the 700 can only be flown at the local air filed so this is why the 500 gets lots of air time.
My Trex 450V2/3 get the most time due to size contraint and batteries. I have 5 batteries for the 450 and two for the 600. I'm scared to cut up with the 600 due to high cost of fixing it. I buy 450 parts in bulk for a fraction of the cost of the 600. I'll usually fly the 450 a couple of times to "warm up" then fly the 600. Then the 450, then the 600, then the 450 again. Now the first battery is charged so I am ready to essentially fly the 450 all day etc...I do love the stability of the 600 though
I have a T500, Logo 500, T700, and T250. I fly the 500 the most with the 250 in a close second. Just love the size and how convenient the smaller birds are.