If you play rather aggressive you probably want Fizz; he has potential to 1-shot almost anyone post-6 and can snowball insanely easily. You do have to play fairly passive the first few levels, though his level 3 all-in is pretty damn good.
But if you like farm champs, Cassio's pretty good for farm champs and has the ability to go insanely aggressive mid-late game, though her early game, while decent, is kinda 'meh'. (She'll prob win most all-ins against non-assassins, but her trading is slightly weaker then most mages, I find.)
Vik is good for going aggressive too, but you'll need good ward coverage as he's fairly squishy and will likely push the lane.