With thanks to mibe420, here is the requested overview of the deadliest monster per floor, from 0.19 on, where "deadliest" = "most player kills". Interestingly, certain uniques made the list.
http://webchat.freenode.net/?channels=%23%23crawl/msg sequell !Lg * recent !boring place=D:1 s=killer
D1 hobgoblin
D2 adder
D3 orc priest ("player ghost" is #2)
D4 ogre
D5 centaur
D6 orc warrior
D7 orc warrior
D8 two-headed ogre
D9 two-headed ogre
D10 Snorg
D11 ugly thing (especially white) (hydrae #2)
D12 ugly thing (hydrae #2, Rupert #3)
D13 centaur warrior (meliai #2)
D14 ugly thing (centaur warrior #2)
D15 ugly thing (meliai #2)
Orc1 orc warrior
Orc2 orc warrior
Lair1 hydrae (spiny frog a distant #2)
Lair2 hydrae (spiny frog a distant #2)
Lair3 hydrae (Rupert a distant #2)
Lair4 hydrae (death yak a distant #2)
Lair5 hydrae (death yak a distant #2)
Lair6 hydrae (death yak a distant #2)
Spider1 wolf spider
Spider2 wolf spider
Spider3 wolf spider
Spider4 spark wasp
Snake1 shock serpent
Snake2 shock serpent
Snake3 shock serpent
Snake4 nagaraja
Shoals1 water nymph
Shoals2 Polyphemus
Shoals3 satyr (water nymph a close #2)
Shoals4 merfolk javelineer
Swamp1 hydrae (#2: alligator)
Swamp2 thorn hunter (#2: hydrae)
Swamp3 thorn hunter (#2: hydrae)
Swamp4 hydrae not including the Lernaean Hydra (who is #2)
Slime1 acid blob
Slime2 acid blob
Slime3 acid blob
Slime4 The Royal Jelly (all via its spawns being pulled upstairs)
Slime5 The Royal Jelly
Elf1 deep elf mage
Elf2 deep elf mage
Elf3 deep elf annihilator
Vaults1 ironheart preserver ('ikiller' summary puts it at #1 with 169 credited kills, however 'killer' only records 12 direct kills)
Vaults2 vault warden
Vaults3 ironheart preserver (see above)
Vaults4 vault warden
Vaults5 titan
Crypt1 curse skull
Crypt2 Khufu (Titans cause more deaths here, but as gammafunk points out, they're not native. Apparently lots of people wait out Okawaru's wrath in Crypt.)
Crypt3 ancient lich
Tomb1 greater mummy
Tomb2 greater mummy
Depths1 stone giant
Depths2 stone giant
Depths3 caustic shrike
Depths4 caustic shrike
Depths5 spark wasp
Zot1 orb of fire
Zot2 orb of fire
Zot3 orb of fire
Zot4 orb of fire
Zot5 orb of fire
Abyss1 small abomination
Abyss2 thrashing horror
Abyss3 starcursed mass
Abyss4 starcursed mass
Abyss5 starcursed mass
Won with: KeAE^Sif, NaWz^Sif, NaTm^Chei, SpEn^Nmlx, GrEE^Qaz, HOFE^Veh, MiBe^Trog, DrFE^Hep, FoFi^Zin, CeHu^Oka, DjFE^Ash, DrIE^Ru, FeSu^Jiy, GnCA^Usk.
In Progress:
Long-term goal: complete the pantheon.