In a tire thread you're likely to get as many helpful responses as you will by asking "which oil is best". Lots of personal experiences by different people, but ultimately you have to try them yourself to find out which is best for you.
Having said that, I do have the Avon Speedmaster and MKII on my 550K, and I really like them. It doesn't rain that much here in Denver so they haven't gotten too much use on wet roads, but when I have been caught in the rain they've given me no reason to doubt their abilities. Oddly enough, the ribbed front tire does better (on this bike) on grooved pavement than the non-ribbed Avon Roadrunners on my 750 do, but that's two different bikes, so it's not the best comparison.