Which sub would you choose?

As someone who's Sold Wilson for years, I think what you have here is a case where you can EASILY spend way more money than you'll possibly get back sonically if you're not careful here! Bass is the single most system set up factored, room placement critical(as well as seating location corespondingly), acoustically challenged, an EXPERIENCE dependent factor!!! You can MOST ASURADLY spend the money you're talking about spending, and get EASILY MUCH BETTER PERFORMANCE and sonics from a much cheaper sub, set up by a knowledgeable, skilled, EXPERIENCED individual!...I can't understate this enough!
I guess what I'm saying is that, from someone who sells the WatchDog, it's a very good woofer by itself. Is it worth what is sells for sonically? In my oppinion, no. But then that's me. If you can afford the money, than I think you should buy one. But make no mistake about it, you won't get $10k+ worth of world class bass out of a single Watchdog, just because you have the woofer!!!!!!...that is correct. World class bass doesn't come from great woofers, it comes from the skilled technician who's putting your sytem together, placing your woofers(or speakers), and calibrating your bass in your room!!
I've seen/heard it hundreds, even thousands of times before! People buy the best products and the most expensive money can buy, and they don't get the performance they're capable of most alsways!...not by a long shot when it comes to bass performance in a given room!
My suggestion might be to buy A COUPLE (or more)excellent high performance, yet more reaonably price woofers, like maybe M&K's excellent MX5000's. Revel's B15 or whatever, even Velodyn's FSR 18's will sufice. I hear excellent things about the Pricy Whise Profounder, which is still way less than a Wilson Woofer if you must pay a ton for ONE WOOFER!!! You could even spend far less on SEVERAL WOOFERS, PROPERLY SET UP OF COURSE(carefull, or Phase cancellation is an issue), and buy like a bunch of Paradigm Servo 15's! Heck, 4 of those would only be a little over $6k new, and you'd have way more to work with sonically! MOre dynamic ease, potentially quicker response, better transient attack, smoother bass response in the room, and a more effortless dynamic overall!..not to mention they're musical subs on their own.
Acually, there's a lot of excellent subs. But I'd probably buy 2 or 3 of the Thiel subs at less than the Wilson's single sub price, and get potentially much better results driving em for L/C/R's, before I bought a $10k sub. Again, just a perspective.
At any rate, do what you need to do. I just don't see the value in the performance that woofer offers for such a rediculous price. Especially when you consider it's only ONE WOOFER!!...which already has it's challenges and draw backs or limited applications effectively.
Also, I need to ask who's setting up and calibrating the woofer for you? And, how exeperienced are you at setting up systems properly? I've just been over to too many audiphiles home's, who own very expensive TRICK subs, only to hear what' DEFINITELY sub-par top caliber bass performance! And we're talking just about every time here!! It's never anything to write home about.
Here, once again, it all comes down to knowing what you're doing with the right gear, especially with woofers and bass performance. If you don't have someone who's going to do it for you, then I HIGHLY SUGGEST you invest some SERIOUS time to learning how to make a subwoofer proplerly integrate and work into your room and system!...this one make take more time to learn than you think for really really good results in small acoustic spaces like these!
Good luck

So now, just for curriosity's sake "Rivercitylad", I would like to know if you STILL plan on buying a Watchdog woofer? Also, has any of what has been said above caused you to possibly rethink your choices?...currious.
Really, a good woofer(or more..even better) properly set up, with good seating location, and with possible parametric EQ'ing, and you would be shocked at what's possible! Even modestly good subwoofers, properly set up and calibrated will do some very good things sonically.
Have fun...

My first thought on the subs you last mentioned, is "great for music potentially, but no grunt for HT!" Everyone's experience here may be different, but I think the woofers you're considering will be more designed with music as a priority in mind. Smaller rooms might do better with more delicate music subs with higher Q factor with HT. But Slamm, impact, and authority might suffer in more agressive and ambitious HT and music set ups! I guess it depends on your needs and applicaitons.
For me, I like subs that can GROWL for HT, and still remain tight and musical. The more expensive Revel B15, M&K MX series subs(depending on room size), Paradigm Servo 15(baragin for HT and music at $1600 new!), And the single standing Infinity Prelude MTS subs with Paramtric EQ (like Revel B15), are dynamight audiphile grade subs overall! For affordable, fast, musical sounding subs for all medium, I think the Servo 15 and NHT Sub 2 are hard to beat for the money!
Good luck