Personally I chose CTC because of the employment opportunities after, that's presuming one doesn't completely balls up the training. Get first time passes and you'll more than likely end up at Easyjet on a flexicrew contract. Not ideal, but it's paid employment. Go to OAA and you'll most likely end up at Ryanair, just bear in mind the 30k for the type rating. Not sure on FTE and their tie-ups, worth checking out past cadets.
Quality of training at CTC I would presume is as good as the other two FTO's, can't compare because I doubt anybody experiences both. Maybe also look at where you want to train. CTC tends to be NZ (Arizona base now operational), OAA is Arizona, FTE Jerez.
If you get onto the Qatar scheme and thats your thing, then go for it. Best to have an airline tie-in if you are fortunate enough. Although there's a big debate on the pro's and con's of the airline schemes, read through them on here to make an informed decision. Im happy with my choice, just do your homework on all three schools. If you are made of the right stuff and don't have problems through the course, chances are you'll end up in a job eventually. Just seems that CTC is a bit quicker than others.