Thurmann has the chance to be really good, but there's a lot of disagreement about how big that chance is. Has displayed feel for 3-4 pitches, but his biggest problem has been weirdly inconsistent velocity. Apparently his velo spiked leading up to the 2013 draft, then tailed off in his first full season, then went back up at the end of the season. Hard to say what's going on there, but there's definite upside. Could be an injury concern, could be a development concern, could be that he just isn't that good. But he'll have starts that really impress scouts, and that counts for something with minor league arms.
Ruiz has a smooth lefty stroke; hits for average and doubles power. Apparently commands the strike zone well. Scouts worry about his bat speed at higher levels, and its weird that he hasn't started turning doubles into homeruns. Still, he's been young for every level through A+, and he's produced so far. Defensively, he was billed as a multi-sport athlete coming out of high school (he was committed to play FB at USC), but apparently he's always been a step slow at 3B and he's a fringy runner. I read some reports last year that thought he'd kind of gained some weight. Sounds like he really just needs to hit the gym, because everyone always agrees that he has good hands and mechanics. Just looks less athletic than he used to be.
Foltynewicz will blow you away with his power arm, but the results have always underwhelmed. He's tinkered around with off-speed offerings, but he's never had great control or command of anything other than his fastball. Throwing 99 mph+ gas with some fringe offerings in a reliever role is probably his outcome, unless the Braves development staff can rework something.
IMO, their ceilings are Ruiz > Folty > Thurmann, but I'm actually a little torn on Thurmann/Folty. Scouting reports always liked Thurmann a lot better than his numbers. Not as much for Folty.
I'm doing this all from memory after following these guys for the last couple years, but Kiley McDaniel at fangraphs did a lot of big writeups recently.