So, what do you think will be the most rare class/skill/weapon combination?

I think it will be something like a Dragon Knight mage or maybe a Nightblade healer.

Nightblade healer would be pretty rare. I don't see much synergy there. You're going to see lots of DKs with fire destruction staves at release. I'll probably roll one.

Those MAY be uncommon, but I wouldn't count on it. Even in Beta there were guys raving about Nightblade healers with Siphon abilities in the battleground. They do have a very PvP feel to them apparently, and the massive crit from stealth bonus makes them able to hold their own too. Perhaps a little too well lol. I compare them with the more tradtional "Shadow Priest" sort of feel.

I'm seeing a very wide mix already from Beta, and it's coming across that many people are being creative and doing there own thing, which is great

I did at the start think all the sorcerers would be pet focussed, but I've seen some awesome results from destruction sorcerers with knockback etc too. Best advice: Do your own thing, and odds are you'll stand out just as you are later on