I have not heard great things about ATP from people who went through their programs. A 141 school is a great thing but it is much more money, and only a small amount of your 52hrs will transfer. Part 61 is probably the best choice.

I have to say it really is not the worst idea to buy a Cessna 150 or Piper Archer for your training. Just about any flight school will allow you to use your own airplane. You'll just have to run the numbers to see if it makes sense, and also take the effort and responsibility of operating an aircraft into account. The greatest advantage I can tell you is that you'll have complete and total control over when you fly and can practice all you want on your own. This will be especially convenient when you are getting to your CAX (commercial) minimums and practicing the maneuvers.
In the end you sell the airplane for a relatively small loss, and move on to get a job teaching.