i have some usa dimebag washburns, a slime and a dimebolt. i also have the only quilt top southern cross washburn ever built as a prototype. i have had 3 usa southern crosses.
i have 5 custom usa dean mlf's they built to my specs, and several usa razorbacks including the last rust and one of the original 7 prototypes they rushed to get finished for namm a month after darrell died.
all of them kick-ass, but i am a bit prejudiced since i love the body style so much.
simply put.....
the deans are like art.
the washburns are like tools or weapons.
dean usa custom shop stuff is awesome because you can make insane demands, and they will try to build them for you.
usa washburns are all fairly rare, and your stuck with what was built since they won't build anything new in that body style.
usa deans will not hold their value. they are worth less than half you paid for it before the guitar is even built.
a $3000 washburn southern cross will always be worth $3000. (if you can avoid the neck joint issues set necks have).
the flame,quilt,spalted,redwood, whatever... tops that dean uses are awesome. they do nice exotic tops. in fact, you can actually provide your own top and they will put it on your guitar.
washburn flame tops are hit and miss.....mostly miss.
if you want that slime color washburn did, don't expect to get it anywhere else than on a usa washburn. trust me on this one.
the first generation usa washburn dimes (flatter volute, razorblade serial number, no buzz fienton) had real issues developing cracks in the clear coat at the neck joint. not structural, but try telling someone else that. all of darrell's are jacked (ask juggernaut). my dimebolt is too. not my slime, as it is a 3rd gen (larger volute, buzz fienton,etc).
the deans will also develop cracks in the neck joint paint if not handled with at least some care. my repair dude cracked the custom paint on one of my favorites just tightening down the floyd claw with it face down in a guitar workstation. man was i pissed. but in reality, that's the nature of a set neck on the explorer/ml body style.....there just isn't much wood above or below the neck for strength.
and leads me to actual BEST answer to your question. which is best, if you want a dimebag guitar, washburn or dean?
neither. order a custom built neck-though gutierrez built to your specs for less than a usa washburn or usa dean. i got mine in september, and have not played any of my washburns or deans since. this is no-bullshit, it's better built, and whatever that guy does to the neck has to be magic (sealer only, no nitro....carbonfiber rods down the neck, etc....). hand built to your specs, even the neck profile. stainless steel frets if you want them. floyd upgrades big block, bullet-proof EVERYTHING!!! (god, i am a whore).
i would never let any of my deans or washburns go, but damned if they are almost just cases in the way of me plugging in my gutierrez custom mlf into my amps at this point.
but if you have to chose, and can afford it, order a usa dean built to your specs and wait.....and wait.....and wait.
or buy a usa washburn dime off ebay and hope the neck joint doesn't get jacked in shipping.