Whats the best paint to use? I have P3 for Warmachine/Hordes and Citadel for Warhammer 40K. Will any of those work or is there a different

one that works better?

Use what you like and works best for you.

I use a combination of Vallejo, Testors Model Master, Tamiya, and craft paints, all for different things.

Good technique and practice do more than buying a particular type of paint.