Boyz!
Pros
Mob rule any mob of more that 11 boyz is fearless, a full mob is 30 boyz
Furious Charge which gives a S 5 attack i believe and 3 I. with 4 attacks on a charge a full mob gets 120 Attacks! i don't care what army that is it'll ruin their day
WAAAAGGHHH! give your boyz fleet of foot for a turn and get in CC early! (turn two usually for me)
Cheap! 6 Points!
lots of shootas and Rokkits! for every 10 boyz you can 1 Heavy weapon (i Don't have my Dex with me now if anyone can post the stats on a big shoota or Rokkit that'd help
)
Cons
No armour. your gonna have to keep your boyz in cover as much as possible, Tau and Necrons shoot can turn a mob of boyz in smoking burnt piles of flesh rather quickly.
bad at shootin, yup like they're loota Friends BS 2
annoying in tight places this might be a personaly thing but placing 30 models in some terrian can be kinda tuff. trenchs ar the first thin that comes to mind for this
Difficult to transport. a full mob won't fit in a trukk and that seriously hinders fighting ability
there's probably more. but i don't have my codex with me right now and did this from memory. feel free to correct me anyone!