First off, let me say that I think the WT550 is a great head! Mine has been fantastic with the exception of having to replace the master volume pot. Fortunately both cabs you mention come in 4 or 8 ohms, and the WT550 does both and runs into 2ohms as well, so you have a lot of options here. I'd suggest going with 4ohm cabs unless you're pretty sure you'll be running more than 2 cabinets off the WT550.
There is much love for the Eden 212XLT, and for good reason. It's a great sounding cab. I owned one for awhile, and loved it. The mids are alot smoother than the 410XLT, and not as scooped and crisp as the 210XST. Would have kept it but I needed to trade it to fund my Aguilar GAS. It pairs great with the WT550, but I always gave 700hz or so a bump just to add a little attitude. I also disconnected the tweeter on my cabinet to let the speakers handle the full frequency of the bass. I don't care for tweeters personally, but the Eden is capable of putting all that brittle glassy high end if that's what you're looking for. I had the 8ohm, and by itself it left me wanting a little in terms of volume, and I always wished I'd bought the 4ohm. Add another cab or get the 4ohm, and you shouldn't have that problem.
I currently use a BassBomb 212, and like it very much as well. This cab has no tweeter (absolutely fine with me). This is also a great sounding cab with a bit more aggressive midrange than the Eden 212XLT. The BassBomb is definitely smaller than the Eden, and is pretty easy to move around. You can totally customize the BassBomb you order: speakers, covering, grill cloth, wood, casters etc. The Eden comes covered in Rat fur and metal grill. So the cool factor goes way up with the BassBomb. At gig volume, I'm really enjoying the sound I get from the BassBomb; plenty of low bass, and a little brighter than my Aguilar DB115s (at least, from what I can remember

long story). I bought mine here on TB from BlowinBlue (Thanks!), but you may have to wait if you buy new from EarCandy.
I have never heard a Bag End that I didn't like, and a couple of S15B's or the D12D are high on my Most Wanted list. Definitely try the Bag Ends if you can.
You might also want to try the Aguilar GS212 or DB212. Both get high marks around here, and Aguilar cabs sounds great with the Eden heads IME.
Good luck!
Cheers,
Clint