Sorry the hear about the 300 gallon. I was really hoping you would end up with that... now you can buy the style you like.
I guess it depends on what you personally like. Reefs dont have a "style" requirement so it just matters on your space and personal taste...
Personally, i like the large tall/wide ones over the long ones. They are not as typical as the long ones and you probably have more room to play with for rock designing, etc. More open water. It just depends. I think if you';re planning on getting tangs, long tanks will probably work better. What kind of style do you personally like? I think most people prefer the long ones over the tall/wide ones.