depends on team comp, i love picking orianna with an initiator like shyvana/malphite/or amumu on my team.
kat, diana, are pretty safe and beastly picks, but you gotta get close
karthus and lux if you wanna crush from a distance
malz/galio are good counterpicks
ap cho mid is hard to push outta lane and has incredible cc, also gets really tanky and bursts REALLY hard
cass and brand are both tons of fun, i'd hold off on lb. she either carries hard or fails hard.
mord/ryze/ap teemo/tf - also all tons of fun
find your style or just buy em all!