Point one: Deathstroke is not only smart and fast (just as batman aka bruce wayne is) but Deathstroke also has a regeneration ability similar to Wolverine... only slightly slower... to put it this way, Deathstroke could even go one on one with Deadpool... and deadpool slaughtered the entire marvel/dc universe singlehandedly... Point two: regardless of preptime, we also have to take into account each persons personal feeling. Batman isnt exactly one for killing someone (granted if this wasnt even the case batman still carries burdens like these and is disturbed by them) But Deathstroke is one of the greatest assassin/super soldiers whose ever lived... And just as an offhand point, Deathstoke can only be killed, ONLY, if someone is using a weapon infused with Carbonadium... which is because of the adamantium infused within him like wolverine... the Carbonadium is capable of nullifying healing factors. So as this points out, I'm for deathstroke here unless Batman just happens to a Carbonadium batarang laying around