If you love your current tone but just want more of it -> add another 2x12.
If you want something a bit different I would go for the TB153 or a 2x15 cab.
I have 2 2x12 cabs and a 2x15 cab.
Using both 2x12's isn't bad or anything I'm just completely hooked on using the 2x15 + one 2x12.
Even when I'm only playing a 4 string or a EADGC setup 5 string the 2x15 really adds to the bottom end.
Everyone has different taste - best bet is to go play through a few cabs at a store and see what fits your style, or would add to it
