Semi-dedis are shared accounts with more resources, but still it doesn't give you any control of the applications, so VPS is better in this respect.
But shared is all I need at the moment, I've already talked to Webhostingbuzz.com support, I'm gonne need Ion Cube for my new site, but they offer ZendOptimizer only, this makes me think about another hosting provider, I'd like someone with the same prices and level of services.