Basically 3 HQs worth taking in the vanilla dex, plus 4 special characters that aren't total shit:
#1 Libby: Run him plain, and always take Null Zone, it's an amazing psychic power, fucking over everything from daemons to seer councils to hammernators. For more info on SM powers read
this.
#2 Captain w/ Bike: The only version of captain I'd ever recommend taking, and this is mainly for the bikes as troops effect. Unless you're running a biker army skip this.
#3 MotF w/ CB: Already been mentioned, he's not really there for the gun though. Yeah S10 AP 1 is nice, but 6 dreads is nicer. Generally something you take to bend the FoC, he's alright in a shooty list but I'd recommend a lib first.
And that concludes HQs, so basically take a Lib. Good Hunting.