Depends on your problems. To get the most out of any you will have to take a fairly wide stance.
I have used all 3 of the briefs you listed.
Preds- I thought they were awesome at the time.. not a lot of stop in them, very easy to use, less carryover, easy to get off, not bad to get on if you know how.
ACE- Good brief. Pretty strong. Lots of rebound. Hard for me to get on and off. Much better carryover than in preds. Not hard to use if you are good at pushing your knees out. Otherwise, you need to really work on the "good girl/bad girl" machines, and practice widening your stance and pushing your knees out hard. You need to do that regardless going into gear, but more so for the ACE because it has a tendency in many lifters to pull their knees in.
BOSS- These were totally worn out (to the point the laminated plys were coming apart and you could feel it was 2ply) and they still gave good carryover. I would guess about like the ACE. I tried a pair of new BOSS once, and they were wicked. I could barely break my hips and go down an inch or 2 with 495... But that will depend on your size/strength. One of my training partners used them well and could hit depth with about 4 plates.
Also, the three briefs you listed are the only legit multi-ply briefs, aside from overkill. Overkill stuff is supposed to be awesome. I have their poly suit and it has wicked pop. Very easy to use, but not enough stopping power for me.
If you want a good/cheap starter brief that still gives good carryover check out centurion briefs. I got more out of them than my preds. My raw strength was about 50lbs weaker when I was in the centurion briefs, and my PR in just briefs was the same in preds or centurion briefs...
If you train alone I would not get the BOSS because everyone has told me they are a bitch to break in. So unless its a used brief, skip the BOSS, IMO.
ACE can be tricky too, go on powerlifting watch and look for powerlifting gyms near you, and start whoring everywhere you can to find a good group. That makes a gigantic difference, and is essential to using gear...especially multi-ply.
Preds/centurions are by far the easiest to use. Based on my experience with the overkill poly suit I would bet his briefs are easy to use too.
If I was training alone.. I would get ACE if you feel ballsy and want a stronger brief, centurion if you want good carryover and fairly easy to use, and preds if you want really easy to use, but little support, and less carryover.