SS has a few really great DC statues (IE: Bane, Cheetah, Batgirl, etc..) but a lot of their DC stuff IMO misses the mark... From questionable female face sculpts to really boring poses and bases... Plus I'm not a fan of Mix Media so that doesn't help either... IMO SS has kind of struggled..
Tweeterhead has had a few mistakes coming out of the gate (Supergirl & Superman) but most of their stuff has been really great... I know WW has the neck seam but unless you place her up high your never gong to see it, so that one I can forgive... But that goofy smile on Supergirl and Superman QC being hit with Kryptonite were major issues IMO.. I think it was also a mistake to copy SS Superman PF's boring base... not sure what Chad was thinking there... but Joker, Harley, The Pooches and Mxyzptlk have been awesome...
XM is doing so really awesome stuff, there only miss so far is Cyborg but they could make changes to him before he releases... Probably the only issues with this line is whether or not your a fan of the Rebirth costumes and the higher price tag. But the detail on their statues is amazing...
As far as how fast Tweeterhead is releasing the statues, I think their pace is fine... they're releasing them a lot faster then XM.... And I doubt TH will lose the DC license, based on all the companies that are making DC stuff, I would say DC is not stingy with their licenses or picky about who has one