Well, I think we talked about this online, but for the sake of anyone else wondering, the best armor for a lvl 80 is the crafted plate, of course. As for the gems, lvl 80 flawless, and you want two of your slots taken by an Immutable and an Inviolate. The third is a mtter of play style. I prefer the various shielding and revenge gems. This is the best I can come up with as far as the PvE side of the house.
As for PvP, I still haven't found a good system to put me on an equal footing, although I have several leads thanks to a friend of mine who enjoys finding the little bugs in combat systems. He was saying stick to lighter armors and use the bunny hop. He actually said stick to cloth and light, but I think he meant Light and Medium. Here you want crafted again, with the first two slots using the same first two gems as your PvE armor, only forget about the damaging gems and concentrate on the magic reducers, specifically they will hit you with slowing down and sticky spells, so Holy and Unholy is my guess (although I haven't researched this yet, so doublecheck me before you go sticking gems in your PvP armor.)
As for weapons, you obviously go for the damage producer in PvE, but this same friend said to use lighter (and faster) weapons for PvP. Apparently, you can only hit people while they're on the ground, so you only have a small window of oppurtunity to hit. It's the fastest twitchy finger, therefore you want something that will give you an edge and not take forever for the swing to complete.
I haven't verified anything I attribute to my friend, as I haven't tried them out. When I do, I will give you an update on whether they work or not, or if anyone tries them before me please post how it well/awful it works.