I think the ideal fridge would be one that was large enough for 4 carboys on the bottom and did not contain a freezer. This way, you could build a wooden shelf half way up to support another 4 carboys, for a total of 8. Unfortunately, I think these are failry hard to come buy.
If space is not a big concern, then a chest freezer will give you more storage for the capacity provided. In my case I have limited horizontal space, so the fridge is the only way to go, not to mention someone was giving it away, which made it a must have .