Meh. ABS is an alright material and it's pretty tough. It's not unlike the stuff cafeteria trays are made out of. A 3D extruded-noodle case will never be as tough as a case made through injection molding due to the inherent sheer weakness between the fused layers. That being said, in my very unscientific and shoddy testing with vice grips, shop scissors and hammers applied to borked pieces, 3D prints are pretty tough to break. A rectangle of say 50x50x5 mm printed with an infill of 50% is surprisingly dense and difficult to crack by hand. I had to use a two pair of vice grips to snap it in half.
As far as protection, I wouldn't count on the ABS providing much in the way of fall protection. Fall protection is all about DV/DT (acceleration), or rather the change in velocity over time. A phone wrapped in a pillow dropped from 1 meter will experience a much lower acceleration than a phone wrapped in a rock when it hits the ground. ABS is definitely squishier than a rock, but it can't compete with something like silicone.
If you're just interested in surface protection, ABS is a pretty solid choice as it's relatively soft and won't bite into the phone finish too much and should offer a bit of protection from your pocket. A 3D printed case won't have quite the same finish that an extruded case has and definitely needs morem cleanup at the end.
I haven't worked much with PLA, but the little that i have worked with it, it appears to be stronger but more brittle (think glass versus steel). Probably not what you want in a case as Apple discovered with their magnificent glass backs...