I enjoy playing against Irwin the most. He's the most challenging and we generally trade wins pretty evenly. However, I don't think he knows what he's doing in the alternate route mode. His strategy on the front half of the board is just as good as normal, but on the back half he never seems to press his advantage once he gets there.
But that's just my impression. Maybe I'm misinterpreting his priorities.
Edit: Yeah, he shows no desire to hold territory up there. He'll complete a course for a piece, rather than holding the rose. He doesn't seem to treat the up-board roses as important places to hold.