Al,

I've used both. I recently did a coffee table with a large carving on the top and I used a 1/2" 3-flute end mill for roughing. It really ate the wood. For other projects I've used a 1/2" ball nose, 1/4" ball nose and 1/4" end mill. It's a matter of matching the bit to the work and the time you have available. The bigger and more aggressive the bit, the faster you can do the roughing pass. For small carvings, the 1/4" ballnose works well.

The big difference between the ballnose and the end mill is the ballnose can get closer to the finishing pass. The end mill leaves things a little rougher for the final pass bit to clean up. That's really the big difference that I've found.