ASIO for me.

I've used both - and both work well without issue.
 
I'd suggest to work with ASIO over WDM, if only because you'll tire of explaining to the clueless that WDM isn't an issue - it's the first thing people suggest as a problem, yet it never is. Most folks don't realize that ASIO uses the kernel drivers internally. This is why you can set your Windows System sound to use the WDM driver, Sonar to use ASIO, and play both at the same time.

That's actually a pretty good reason. Part of the reason I'm getting a MOTU unit is that I have problems with EastWest Play and nobody can get over my audio interface since it is "consumer" even though it has the same DSP chip used in the EMU units. I was thinking of getting a Matrox, AJA, or Blackmagic unit (I do audio over HDMI) but those are known to the pro video community, not the pro audio community, despite the fact that the audio works the same in both. So I went with MOTU because it looks like a nice unit, and because it is the most likely to cause audio people to STFU and actually look for what the problem might be and not fixate on brand name.
 
So I think you are right about ASIO for that reason. I personally don't care, unless one actually works better or worse, but I don't want people getting distracted because they don't like WASAPI/WaveRT/WDM.
 
The HDX-SDI is currently sitting under my desk, so we'll see how things work tonight. Hopefully well. I'm hoping it works well as both a pro card and a general audio card for games n' such so I can ditch the Auzentech. While there's no reason I can't have two cards, one is more convenient and the HDX-SDI has the advantage of outputting in almost any format, so I can mix and match gear, if I should decide I wish to (it does HDMI embedded, HD-SDI embedded, balanced analogue, and AES/EBU, 8 channels in all cases).

Heh, if you ask me, MOTU interfaces are one of the best unsung open secrets out there. You don't hear much about them because, well, MOTU has a Mac-ish history (which reminds one of difficult Mac-only support type vendors). So, IMO, let 'em all fight over their Focusrites, Presonus', Rolands, RME's, etc -they can't outclass MOTU in it's price range, dollar for dollar, quality or otherwise. They're not cheap, nor are they overly expensive. You don't hear much from MOTU users because, well, we're generally not having problems. No news is good news.

Their Mactarded past was something that worried me for sure :). While there's no reason a company can't do good on both platforms, I've observed that often isn't the case. Their developers know one platform much better and thus view the other one as doing things "wrong" and make their software incorrect and poorly performing as a result.

I get better performance/lower latency with ASIO.

I guess I spoke too soon.  I continue to get Blue Screen after Blue Screen using the UltraLite-mk3 with my ASUS laptop.  It was really working well for a few hours, but this morning...back to Blue Screens :-(
 
A bunch of Windows Updates got installed overnight...don't know if that could have something to do with my issue.  But as of now, I'm having no luck at all.

Things are not off to a good start. The HDX-SDI is defective out of the box, or at least I assume so. It doesn't seem to power on. If it is powering on, it is being real sneaky and giving no indication. Also seems to be good at hard locking the system. I'll call MOTU tomorrow and see if there's anything to look at, but I have to imagine it is broken.
 
I have a feeling this is going to turn in to a month+ project given that everything is East Coast so RMAs are likely to take forever :P.

Ouch! Is the laptop running Win 8, and/or is the USB port a USB-3 port? Those seem to be the major issues these days with interfaces, not particular to any one brand.

Me? Desktop, running 8, and not using USB, the HDX-SDI is PCI express.