All guardians can learn the same skills, it all depends on the slots.
Skunk and cure being the most useful basic skills for guardian.
Rust and magic melt down would be helpful.
You can teach your guardian 2nd job moves of a certain type, the one from MS.
If you don't plan to get a MS rune stone, it almost doesn't matter as long as you have cure, rust, skunk and MM. But if you wanna get a 2nd job skill for it...
Is your buffalo pure or hybrid?
If it is hybrid, I'd say teach it the sense type stone. You will need at least 5 slots for it to learn shield breaker. It is VERY good if you use guard break+faint together with it.
If you are pure, I'd say teach your guardian the power type stone and let it learn guard break. That way, all of your melee attacks should land.
At least this works for CT bosses. To be honest I don't boss hunt normal bosses that often.