First off disclaimer: I don't own a Chan. With that said at the Carolina Freeride I had a solid 2 hours of ride time on a Chan with the surf plate powered by a limited 701 setup back to back with a -4 SF with nearly the same 701 limited drivetrain. They are both superior riding hulls, however, if I had to pick one for surf it would be the SF and here's why. The #1 issue I had was not being able to shift my wait over the hull while standing in a surf stance. I never felt balanced when cruising down and along side the face of a crashing wave. The Chan just flat out needs a front foot hold for surf, and their is plenty of room to add one. If feels like the SF will keep up righting itself with a wave curling on you acting like it grabs the ski and then lets go, grabs lets go, and so on. The Chan tends to roll more with the wave seaming as if its sitting lower in the water as when the wave starts to push you around it never lets go. I think this can be corrected again with a front foot hold shifting the center of gravity. When riding the 2 ski's I noticed I never got fatigued when riding the SF, I was well balanced on it and didn't have to fight it that much. After the first 30minutes on the Chan I had to get out past the breakers and take a short float break.
Although not part of your question, I felt the Chan railed 100x better than the SF and was all-around a funner play boat in the small rollers and flat inlet riding even with a little 701 in it. I feel a front foothold would make a night and day difference with the Chan's balance in the surf. Bottom line: If the Chan and the SF were the same price and because I do a little of both flat and surf I would buy a Chan and add a front foot hold and have a solid all round boat. If I never plan on riding flat SF is the way to go.