I have an Arceus in soulsilver and i have all of the plates which is the best arceus type?
There is no best type, really. I usually just switch them depending on what situation I'm in. However, steel type has more resistances than any other type, and ground is super-effective against the most types.
I just need a good type and moveset to sweep teams. Suggestions?
do dragon, dragons kill everything
Steel is a decent choice as there aren't a drastic amount of Fire, Fighting or Ground Pokémon in HeartGold/SoulSilver, and you can use a Swords Dance / Extremespeed / Iron Head / Earthquake set which will do incredibly well.
If you've got a Special Arceus (as in it's SAtk is greater than it's Atk) then you can use a Dragon plate and go Calm Mind, Judgement (Dragon Pulse until Lv100), Thunderbolt and Ice Beam, or Flamethrower and Earth Power.
My vote would've been ??? Type, if there was a Plate for it...
Otherwise, Dragon. Just my preference. Dragons are cool.
i'd go with most of the suggestions here; steel or dragon. but! if you want more power with the incredibly useful extreme speed, let it get stab off of it. i've fought against a normal typed extreme speed acreus, and from what i can tell you, i was in awe at how great it swept.