For your first army, it's always best to just grab what looks cool to you and go from there.
So go for the ones that look cool.
Then about 100 mistakes and a couple of hundred dollars down the line... you'll know what you need to do right next time
Dark Angels 1750 win/loss Record
Win - 23 (Belial helped wreck Ryan's puny Eldar)
Loss - 13 (Brice's Necrons wiped me)
Draw - 2 (The 13th hold out in alpha take and hold)