So far, the best tire I've used is the Bridgestone 203 in 90/100x21. It's quite a bit better than the 403 in sand and coarse, sandy gravel, silt, etc. I can much more often recover from the terminal front end push the '06 is prone to if not managed properly. The 203 stands out against other "soft terrain" tires in that it works well on much harder soils than most of them will, which makes it more versatile.
It depends whether you ride more in the higher or lower deserts, to a degree. The lower deserts have their rocky stuff and all, but they have a lot more of the softer, deeper sand/gravel/silt stuff the the higher deserts, which tend to have less sand and more rock, and more of something that looks like real dirt. IMO, the 203 covers both well and does sand much better, while the 403 is better suited to the higher deserts and rocky dirt
I liked the MX51 on a groomed track, but it was unpredictable on blue groove clay, and disappointing in the soft stuff. As to the Maxxis, I ran a lot of their rear tires to the bone back when. The "big" tire back then was the Dunlop 756. It worked good, but wore out if you so much as looked at it. The Maxxis IT rear cost 15% less, had better straight line traction, and lasted 3 times as long. But the IT front sucked, and now they are as expensive as premium tires most of the time. The ST was better, but neither tire was very supple, and their desert tires are ridiculously heavy and hard.