I was a Matco locking flex user for a few years, and I really liked the ratchets. I wound up switching to Snap-on because I found the Matco lock button unreasonably hard to operate, on both the 3/8" and 1/4" ratchets.
I've owned my Snap-on locking flex ratchets (1/2", 3/8", and 1/4") for 3 years now, and none of them has any play/slop. The only one that has given me any trouble was the 3/8", which wouldn't stay in the unlocked position. My dealer swapped out the locking assembly and it's been zero problems since. Some don't like the Snap-on locking flex ratchets because they think the locking "wart" on the handle is ugly, whereas the Matco locking switch is almost flush with the head of the ratchet, and in theory gives you better access. I say in theory because I've never found the locking switch on any of my Snap-on locking flex ratchets to be the reason I couldn't get to a fastener. I also like the fact that I can lock/unlock the Snap-on without looking at it, like when you have to snake your hand into some cranny and wrench by feel only. That's not something I was able to do with my Matco ratchets. I will also add that in my experience, the Snap-on locking flex felt stronger in terms of "will this ratchet hold the angle that I locked it in while reefing on it."