both would be great to have, but if I had to choose one I'd go for the 8 ft tank. More stunning IMO. but if I was to keep fish that needed a large turning circle such as gars or arowanas Id go for the wider tank. The longer tank would be better at housing more of the smaller types of fish because it gives them more of a spacial seperation, some territory to claim. In terms of practicality, the 8 ft tank would probably take up a whole wall of a room while the wider tank would stick out more, Id almost want to have such a tank in the middle of a room so that I can walk around it.
The 60" would be to short for any arowana over 24", not that the 8 footer would be any better as it is to narrow for any aro over 24".