My experience is all 26" and 650b, YMMV!
I'm not a fan of the Maxxis tires; I find they have a softer side wall and if using them tubeless they tend to be a bit squirmy at low presures. They are also fat tires, coming in well over weight. That said I do like to train on them, as they are dirt cheap here in Australia.
The Crossmark is an alright rear tire, but not something I would use on the front. I modified mine by cutting off the cylindrical knobs ala http://forums.mtbr.com/wheels-tires/maxxis-crossmark-snipping-tweaking-816662.html
. I found performing the modifcation greatly improved the tires bite particularly on our sandy climbs around here. I do like the look of the Maxxis Aspen also and may give that a try when the time comes.
For racing, I am using an age old combination 2.25 Rocket Ron on the front, and a 2.25 Racing Ralph on the rear, I find this combo works quite well and rolls pretty quick and grips well in most conditions that I encounter when racing (usually loose and dry or rocky conditions).
Edit: Kenda's were fantastic back in the day, I used to run a Karma rear and Nevegal rear with great success; I am disapointed their flagship tires are no longer lightweights and 26" has been all but forgoten as they were a great tire at a great value price.