probably a master of archery, one handed (dagger), pickpocket (to pickpocket poisons) and sneak

If we make a competition regarding who can successfully complete the objective of any assassination (i.e. killing the target), I am quite sure that my 2-handed wielding warrior in heavy armour will be just as successful as your dagger-wielding, poison-expert.

If the target is dead and you get away then your an assassin the means of achieving that as long as its effective and efficient are unimportant. Personally I rather like getting out of sight and casting frenzy on the target or someone nearby.

I wish everybody could answer like that