I have owned 3 OTTB's, and ridden lots of others. Personally, I love them! But each horse is completely different...it's ridiculous when people say "all OTTB's are hot", "all Thoroughbreds are hard keepers", and other generalizations. Definitely consider getting a Thoroughbred straight off the track, as like other people have said, a lot of the rescues have had serious injuries that will make them lame and unsuitable for competitive jumping.
Look at lots of different horses before choosing one!! Right now I have an OTTB who is 16.2 hands, really light boned and lightly muscled. He's also extremely hot, and a beautiful mover...although he sucks at jumping. :P My OTTB mare is 15 hands, built almost like a Quarter Horse (stocky and muscular, shorter legs). She's a good jumper, but isn't a flashy mover at all...she's more suited for barrel racing and stuff like that. My third Thoroughbred is a 4yo, and she never raced. She's about 15 hands, and is a phenomenal jumper! But she's a lot to handle.
Each horse is completely unique. All OTTB's are not good jumpers... so choose yours by his personal talent. I'm sure you can find one who's sound and retrained already that is exactly what you're looking for, if you take your time.
OTTB's are the best, in my opinion!