If these pianos were new, I would rate them as follows:
1. Baldwin
2. Cable
3. Kimball
Since they are not new, this rating goes out the window!
Here are my suggestions for you:
1. Ask for the serial number on each piano, and I can gave you the exact year it was built. Don't take the seller's word for it!
2. Play each piano and make sure every key plays correctly. Play each key one at a time.
3. What condition is the finish in? Is it scratched or badly marked up? Are there pieces missing?
4. Open up the top and look inside. Are there any strings missing or hammers missing? Do the hammers have deep "teeth' marks, or are they basically smooth?
5. Is there a crack showing in the pinblock? This is the wood at the top where the pins that hold the strings go in. If so, the piano will never hold a tune!
6. Is the soundboard cracked? This would cause the piano to play with a buzz sound on certain notes.
7. When was the last time the piano was tuned? Since the seller tunes pianos, I assume this was done recently.
note: Since the seller is a tuner, have him/her agree to tune your piano as part of the deal after it's been in your home for a month!
I hope this is helpful!