Alpha 4 is very good. Not had any problems yet and I'm really happy the course positioning works quickly.
The switch to TFT was always going to happen as the few companies that produce OLED screens just can't keep up with demand. That's why the Nexus One, HTC Desire etc moved from OLED to SLCD. The TFT in the new San Francisco is as good as the OLED and actually has a better touch controller and sharper text. The only downside is the backlight really but after a few days you won't notice it. Nobody has reported worse battery life.
The Orange San Francisco is still a bargain even with TFT. It has good specs that handle Froyo absolutely fine. Oh and Gingerbread is currently being ported