I second dante's post. Take someone who is expereince in OTTB's with you to look at any potential prospects. They will most definitely see things that you don't.
I have an OTTB who was off the track for a year before I got him, but he was on the track for 8. I think the year of rest permanently screwed him up....although he does like to work, and has excellent ground manners, he has a horrible attitude from being left alone in a pasture with three other horses.
I had the basic flexion tests done on my guy, but he's also just going to be a trail horse. I was there for his vacc's and his teeth floating, and also I was there when he had his feet done right before coming to me. However, I know that he probably has a myriad of injuries that I will probably never know about, because the track owners didn't give us his vet records. Other than some stiffness caused by arthritis in his back legs, he's good as gold for light work/riding.
If you really plan on doing serious work/training with your horse, I would pass on the gelding with the ankle injury, unless you can see x-rays done by the other owners, and have another vet evaluate them for soundness issues that might come up (I say your vet, because the owners vet might be trying to sell you something. You never know).
Either horse you choose, plan on giving them some down time to get used to lower energy feed, as well as get them used to coming off whatever steriods they may be on. How much time depends on the horses temperament and how well they adjust.