The big game philosophy difference is that the BM is designed to get in the trenches with your minions. You get buffs for both of you by attacking and your companions will often buff you too. By contrast, the Necromancer is much more interested in using her minions as a resource. She has several active summoning skills that will have you standing back a lot more.
The big BM build right now is squirrels (it's wolves but converted with the helmet Ziz made). You get a sizable squirrel army and go to town. My favorite way to do BM is to get Raptor, Bear and Sabertooth but it isn't very good right now.
My favorite Necro build right now is zombies. I like taking the jump node and it's like having a bunch of leaping banelings.
If I had to pick between the two, I'd probably go with Necro myself.
If you like the 1 single minion style, the Falconer will be coming with 1.0 that is a new style of minion build for LE.