No one will care or look into how you trained for your CFI, so you do not have to worry about using a 152 and a Cessna RG. Also, you keep saying you do not want to rush your CFI, but ATP will rush your CFI. ATP will get you done in two weeks. It could take two weeks just to get an FAA examiner at the FBO. If you are worried about getting your CFI at an FBO vs. a pilot mill, don't be. Getting your CFI at ATP will only help you if you want to work for ATP. Many threads on that. Expect a minimum 8 hour day 7 days a week for $1500 a month. No one else cares where you get it. There are some places that will like the fact that you went to ATP, and there are others, like the place that I work, that will look down on you with a wet CFI from ATP (Too many bad experiences with recent graduates). The best thing to do is go to the place that feels right for you.