Hi Jim. I've used both ABS and PLA. ABS prints and layers more cleanly, but lifts off the print bed something fierce. Still playing around with bed heating, and modifying object design to counteract that. It also smells pretty bad, even tho the UpMini is enclosed, and I've built a moderate surround cover with an exhaust fan, and it's right by a window, after a 6-hour print, the air was acrid. PLA, can barely sense anything, even after a 9-hour print I just did. But I've had trouble with PLA being too stiff to feed well. The Tiertime branded PLA, made/certified by the same maker as the printer, feeds great. I'm about to try Foxsmart PLA.
Pic shows latest project, an egg-cracking platform. On the left, first draft, much too small; on the right, current version, just out of the printer. Shows the other thing about PLA, it gets stringy. Took a lot of sanding to clean.