If you are going for PVP, S/S is probably the best, since the skill sword defense gives you a temporary boost of something like 80% def, and reflects some dmg as well. Just because of that alone, some ppl say S/S is best for PVP. Maces, on the other hand, have a lot of stuns associated with their skills. Not as commonly used, but still pretty good. You can buy 2moon dil to change your items.
Axes have the blow ability on some skills, which directly attacks HP (bypasses shield). If the shield is already depleted, or when attacking a NPC monster, it'll just do extra damage. You will see lots of A/S PVPers. You can buy 2moons gold service from our site when you do not have time to level up your character.
Any 2h weapon is good for PVP or PVE, since they can use both single weapons skills and 2h weapon skills. The 2h skill genocide hits great, and even lowers opponents defense. 2h weapons do require more str or whatever that their 1h counterparts to use though, but nothing excessive. The only way it would not work is if you had S/S and 2h axe; the stat requirements are so different, you would be wasting points just to use both weapons in 2Moons.