I've flown with all three for one reason or another, and would also recommend Billins FOR WHAT YOU WANT. On the other hand, if you are planning a CPL, go with Bonus as they are a well regarded CPL school and it gives you a chance to decide if you like them or not.
Billins has a C150 and a couple of Grumman AA5s, so either way, you'll get a change from the PA28. I'm biased and prefer the AA5 (having about 140 hours in PA28s, it took me about 2 hour to become a thorough Grumman convert), but they are more expensive than the Cessna.
Bonus is likely to use a PA38, which I confess I do have a soft spot for as an aeroplane, particularly for training - although many people don't like them much. But make your own mind up.
I agree, Billins will be cheaper, and is a lot less formal. On the other hand Bonus will get you closer to the CPL training environment if you're heading in that direction anyway.
You may detect that I'm avoiding mentioning CFT. That is correct, I am.
G