One 240 gallon tank. Two smaller tanks would be nice, but I'd rather take care of just one big tank. More tanks is more hassle and takes up more space. A 240 gallon can go a long way if you stock it right.
Or you can do what any true MonsterFishKeeper would and get two 240s!
Nah I'm just kidding, but I would go for the one 240 like others had stated before you can fit larger fish in a 240 and your less likely to maybe have to up grade with your fish. Also on your question I highlighted there, well it really all depends actually a 150 can be a number of widths. Can you tells us the dimensions of the tanks?
two 150's for sure. Could have two different biotopes, or at least two different types of predators that wouldn't stay together...
or more than likely for me... I would have two different crenicichla.
the 240.. cuz then i could always get another one and double stack them .. the 150s would be nice accent tanks though.. i could let my gf plant them and that would shut her up prettymuch forever