If you are looking to SLI now or in the near future I'd say to get the reference model (Yes, it does look pretty sleek), but if you are going to be using only a single GPU I'd just go with the ACX. It'll give you better cooling performance, but I guess you could choose either. The reference model isn't that bad in cooling, but as a personal preference the SC ACX is better. Just be sure to maintain good airflow in your case.
Don't worry, ether one will be fine. It's your choice.