Great question and one that I've struggled with. YMMV, but I've had the following experience with leashes v brakes:
1) original Dynafit tech bindings had leashes. No issues with daily usage but I had one big ragdoll where I would have rather not had to ski bash me on the head (backcountry, no helmet)
2) G3 targa tele bindings w leashes….no issues but then again, no real release when things start to slide.
3) Plum Guide bindings – first used leashes….had a massive ragdoll on an exit out of a chute and now possess a nice scar on my head that my wife thinks looks hot. Not. Tried the forward facing Plum bindings….my experience was fairly positive however I did have one in-resort release where the forward facing brake legs caused one ski to literally launch airboard do the initial "grab".
4) now using G3 Ion's – love them. Using brakes and so far, only issue has been one ski that was lost under about 100 cms of snow that took quite a while to find. But would I rather look for a ski than get my head bashed in again attached to a leash. Yes. And I find it easier to lock into the skis w/ a brake when I'm on something really steep where f-ing around w my skis isn't an option. I also felt like fiddling with a leash on steeps fell into the f-ing around category (recognizing that I could have not used the leash on steeper terrain). I ski w/ DIN set high so should have no releases so could have gotten away w/ no leash but I hate faffing so just like having brakes and no worries (other than snow caking…).
My two cents worth.
b.