Unless you are using the Bi-amp feature, follow jimmy M and get two of the same cab/brand. It will sound better and be much louder than two different brand/size cabs.
Believe me, I used to have the Eden 212XLT and Eden 410XLT running with a power amp. It sounded decent, but as soon as I removed the 212 and added an identical 410xlt - the tone became punchier, louder, clearer, you name it. Some mismatched cabs can sound great together, but you could be spending way too much time trying to figure that out.
I suggest a Markbass 410 of some sort. Try some out and go from there. We don't know what you want tone wise and you better off getting two of the same cab THAT YOU LIKE.