Probably most of the unarmored foes. Heavily armored foes like Death Claws still take a couple of hits from a Ballistic Fist. Now if there were unarmored foes with tons and tons of HP, I think higher DPS would be better than high frontloaded damage. But there's none that I know of.
I think Oh Baby is the best for melee and Ballistic Fist for unarmed. I prefer the fist because it's more efficient in VATS.
Hrm don't seem be able to 1hit many things. For example I just cleaned out the Omertas, and all their gaurds took 2 hits to kill unless I got a crit (either Oh Baby or the Ballistic Fist). And yes that's with a power attack. I'm at lvl 25 with 100 in both Melee and Unarmed and all the melee relevant perks, and 10 strength, so short of drugs my 1hit damage isn't going to go up.
So close combat seems pretty bad, frankly. I guess I should have expected it to be a lot worse than guns though. It's fine vs everything humanoid, but deathclaws are a huge pain, since you die in 3 hits (even in full PA), so anything past 1 deathclaw is pretty much GG.