This was pretty much exactly what I was going to say when I read the OP, except to add that I would pick Tauros since IMO it's generally easier to go offensive in-game than defensive or stall-y, but it's your call.Tauros if you want an offensive Pokemon, Miltank if you want something more defensive. They both have pros and cons, it's all up to what your team needs.
Oh what a brand new idea.Nobody ever thought of that!Miltank, but to stray off-topic:
I saw this FakeMon that had this baby cow. Females turned into Miltank and Males became Tauros.