well if your levelling,
i'd say dont go down assassination until 55. combat will be OP compared to assassination until at least 50 if not 55.
personally i waited until outlands and levelled 60-70 as mutilate and it was much easier imo. less dps in instances but a lot more control for solo levelling. you can keep the mob stunned over half the fight and that means less downtime. also easier to get good daggers in outlands.
http://www.wowhead.com/?talent=fMecoxgsVzVoZV0ec0h
this is the build i used. its nice cause you can PVP w/it very well. the extra CPs from initative help with stunlocks.
you open a fight with CS, get 1 DP on, mutilate, wait about 7 seconds for energy, then KS > double mutilate. almost everything will die at this point and if its not dead you have 5 CPs to envenom with to finish it off. there are some things you can move around but in pvp mutilate you want to have opportunity in all cases. improved KS and find weakness make your muts much stronger and are definately worth it.
in pvp make sure you use a mouse and do a jump/turn/mutilate in the air.
anyways, a few notes about your build, always take ruthelessness. for levelling you dont need 5/5 vile poisons and 5/5 improved poisons, pick one or the other really. having both is more of a pvp or arena thing. quick recovery is more of a pvp talent, but improved KS is going to do a lot more for your levelling. improved eviscerate is more of a pvp talent and you shouldnt pick it up for levelling or raids.
also in my build, remorseless strikes gets removed when you hit 70.
if your planning on raiding mut you do something like this http://www.wowhead.com/?talent=f0efoxTsVzVohfVb0V
again vile and improved poisons, pick one or the other. my DPS spreadsheet says getting 5/5 improved with DP on mainhand and IP on offhand is best for DPS.
you can switch 2/2 murder for 2/2 quick recovery if you want.
first row of combat is optional. i like gouge for the utility it has. you always want SnD, DW spec, and precision in a raid build.
Edited, Jun 22nd 2008 10:09pm by EnthalpyTheBurninator