I vote for R. It has a certain depth, that the other letters don't have.
It has a certain sound: RrrrrrrrrrrrrrrrrrrrRrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrRrrrrrrrrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrRrrrrrrrrrrrrrrrrrrrRRrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrRRRRrrrrrrrrRRrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr rrrrrrrrR. It's like combinding the eternal future with the past, in a post-apocalyptic way of saying "Hi. How are you?", with a scottish accent before it was invented.
Pretend you are a lawyer, but with the feet of a flower, which hasn't blossomed before sunrise.
You walk down a alley. The meadow smells sweetly of clover. RRRrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrRRrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrRrrrrrrrrrrrrr.