Thats an easy but hard choice. Easy in that I only like fish that get 18" or bigger, but hard because while you get more stocking options you also loose stocking options. Like take my community for example, they are kinda small "so far" for my taste I would like to toss something bigger in but they would get eaten.
I say two a 500 and two 250 if I had my choice, you could have some nice preds in the 500 a nice community and one other tank to do species tank.