I did a 757 rating, although the A320 is looking very good at the moment. If I'm honest then really whatever rating you do you will find a job. As you're paying then think about what type of flying you would like to do or where you would like to be based. If you have set your heart on being based in the UK and flying 1-2hr multi sector days then a low cost is a good option etc....
What ever people say about the pro's and con's of paying for a rating the main thing is this. You want to be an airline pilot, and you have tried all the normal avenues like instructing and networking. Then some guys from your flight school start flying 737's / A320's because they paid for a type rating. Now they are being paid £35,000 per year and doing the job you would love and you are still doing the job that pays £10,000 and flying a C152.
You have to do whats best for you, whatever your choice just look at the facts and then decide. Best of luck whatever you choose