You are asking the question wrong. What you want to know is, what is cooler: a Dalek army or an Arachnid army? I would totally say the bugs but I've never watched Doctor Who. Also if you go for the bugs you'll be competing with the Pwnies over the "utterly alien swarm army" cliché.
Remus: Harry... I'm a werewolf.
Harry: Are you fucking serious?
Remus: Well yes, but I don't see how that applies here.