I believe a chest freezer will normally have more space to hold more kegs(thats a plus). Generally, they will be wider than tall. Fridges hold less kegs and are taller than wide. Both units can be controlled by an external temp controller. Other than different size configurations, a chest freezer may withstand lower temps for longer(an idea I just thought of). I recommend visiting a local Best Buy store and compare and contrast between the two. See what works best for your homebrewery. Finally, used fridges may be cheaper and easier to pick up. Good Luck!
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 .