1mag,
I am a flying instructor and an FO at London City. All of the schools you listed need to be visited to see where you are most comfortable. Remember, you are there for quite a while and you must be relaxed.
I went modular at Bournemouth, Professional Air Training, as I felt very unimpressed with OAT and Cabair. PATwere very helpful, compared to OAT who due to large numbers, forget the individual. The sales is very heavy, but it takes a step back to see through it. Don't just believe all you hear, get in and ask probing questions. I didn't fancy training in the desert in temps over 45 deg. I asked the sales bod at what piont did they stop flying......45 deg. That means that the cockpit is way above that, with no air-con. Nuts to that.....
Cabair will tell you what you want to hear re-jobs. Again, ask for previous students e-mail to get the truth. OAT claim to have a recruitment team, but I hear you are just forgotton once you have parted with you cash.
Expect nothing, and allow enough money to fund a bond / TR. I didn't have to, but many do. If I went to Easy with my Turbo Prop hours, I would still need to font the money for a TR. Needless to say, I won't be applying to them. I would recommend you instruct for 6 months or so. It is really good fun and gives you exceptionl handeling skills on those rough days, while maturing you very quickly.
There are no guaranteed jobs. Luck and knowing the right person at the right time is vital. Most airlines get 50+ CV's per week, most low houred. It is luck if they pick yours.
Example: On my sim check, the other bloke being checked had 5000hrs flying all sorts of twins. He didn't get the job and at the time I was on 450hrs with a bit of instructing. The ops dest is littered with mugs with pilots details on. Clever idea, but they are just laughed at.
Not trying to pi## on your strawberries, but there is a reality to the dream, and lots don't make it, having blown money they have to pay back. Some get the FATPL and never find work becauce they don't chase hard enough. Don't pay for a TR without a written offer of a job. I know 2 people who paid for 737 TR's and 1 is instructing, the other is back in IT.
Good luck!
Don't listen to bull and be suckered into a bad deal. You are the customer so if you are not happy, tell them. Go a bad instructor, get rid.