Oakley A frames with the persimmons lense is the most versatile / bang for the buck. Like the picture below -
If you get the iridium you could be screwed if you find yourself stuck in flat light, shadows or night riding conditions. The best bet is to get 2 pairs of oakley a frames - one with each lense. Of if money is tight get the iridium and buy an extra persimmons lense.
Im sooo sold on the A frames I've been wearing them for about 7 years now. I've got 3 pair.
The O frames are wider, and you can't change the lense out like you can with A Frames.