[Justin Pasternak]

I was wondering which weapon such as a mace, flail, battle axe or war hammer would be best to break plate armor?

[Richard Fay]

Hello Justin!
The shortest answer to your question would be the answer to this question:
which are you most skilled in using?
Of course, other factors such as construction of each individual weapon would also effect it's armour-breaking abilities (a simple agricultural flail impressed into service might not make as many holes as one with all those nasty spikes).
By the way, hello all!
Richard Fay