Both use the cheapo Omron micro-switches
for their buttons, so this is by far the weakest link in the damned things.
If you're right-handed I'd say get the DA because it has a much better shape. Their driver is a pretty horrible memory leaking abomination though, so I'd avoid installing it if you don't need to remap buttons and don't care about 3500DPI (it defaults to 1800DPI without the driver, IIRC).
I speak from personal experience. I could also provide a razerblueprints.net link regarding the razerhid.exe memory leak, but the site has been down for quite some time.
If you're left-handed you could get the Left-Handed Edition DA, but I'd advise against it because the buttons are also physically inverted, so you NEED the drivers to remap them (is there any left-hander out there who actually inverts the buttons?). So I'd say go for the Sensei in this case.
My Sensei, as you can see from the link above, is failing miserably due to the Omron switches, and the coat is also wearing out. It does have pretty good tracking though, I'll give it that. The DA also has great tracking.
But to be fair, I've had a Left-Hand DA and now I have a Sensei, and I'm disappointed with both. So pick your poison, I guess.
EDIT: As for the mousepad, I'm using a QcK+ which works just fine. Most people say the Sensei tracks better with hard surface pads though (I can't say because I didn't test it). Cloth pads do last longer, so you might want to consider this as well.Edited by vittau - 11/24/12 at 4:59pm