I'm not a huge fan of open-hole altos myself, mainly due to my tiny, feminine hands. I simply have a very difficult time stretching my fingers to fully cover the holes.
However, some people say that the open-hole models have better intonation and sound less stuffy, since there's more room for air to escape. It's probably very much a personal decision.
However, most premium-line altos (such as LeBlanc models) are closed-hole, so that might mean something right there.