My guess would be whoever gets the best weather!
Looks like, as usual, the weather is being a big factor again at a British Open. I am almost tempted to drop some money on Phil Mickelson, but the weather report for today at Royal Troon is only marginally better than the weather from yesterday. It could become a bit of a crap shoot and I suspect that we will see some fairly average scores again today... lot's of rounds of 1 or 2 under I would think.