1- The disadvantage of wax is that it is not as slippery as petroleum-based products.
2- I've been using Dumonde Tech Lube Lite, which puts a plastic film on the chain parts to make them slippery. I don't know how much mileage I could get out of it, but I re-lube at least every 300 miles "just because". Rain doesn't seem to affect the mileage. What I like about it is that I never have to use degreaser. To clean the chain I use soap and water; works great, and I always have a clean shinny chain.