My current favorite would be the 221, it's so darn cute.
The machine I want is a 15-88. In the spring I found a treadle with a 127 in it, I don't think I'm ever going to really love that machine, I find that long bobbin hard to use. I want the reverse and ability to drop the feeds dogs on the 15s.
I have a 15-91 from a recent trade, I've replaced the handwheel and bought a reproduction bobbin winder and it seems to work okay using a hand crank, I haven't tried it in the treadle yet. I'd still love to have a true 88 though.
I thought I had found one this morning, it was so promising. The seller said it had been in a treadle and had a motor added. He only had one photo but after asking him questions about the motor position and the belt on the handwheel it certainly seemed to be a motorized 88. Nope, it had a potted motor. I was so disappointed. He tried to get me to buy it anyway and cut the price in half (already cheap!) but I passed.