I would say the following:
1v1 (gen 4 and 5)
1v1 Challenge Cup
I would say no Dream world because no one even knows if all the pokemon will be released yet, and to me it seems pointless. not to mention it is extremely similar to standard OU with Shandera banned. Only ditto and techniloom make it different, which doesn't warrant a metagame. I've gotten to the finals of several DW tours with my wifi team, so I dont think its enough of a tier to advocate its own tier.
ADV OU is because ADV is actually played but I think Ubers and UU are barely played at all, in comparison to OU, which is played much more, like in all generations.
Challenge cup is immensely fun and deserves a ladder, so people can find other battlers. Its very annoying when people randomly challenge you, and this is an easier way to find battles.
I don't have Gen 5 UU because you need usage statistics and I dont trust PO's UU tiers. Why not? Latias and Mew were UU for the longest time. Anyone who does that cant be reliable, since it is based on usage statistics. I would trust Smogon, but it doesn't have UU yet. We could make our own UU when we have more people, but I don't see enough of a base to gets alot of usage statistics.
middle cup gen 4
All the stuff badal mentioned and I didn't
Our own tiers (we could be the only people to start out without a ban list)