I still don't know what to choose from A2hosting.com - semi-dedi or reseller account?
What is more preferable in term of earning money?

Well, I'm sure you can upgrade from reseller to semi-dedicated, so why not start with reseller

Are you going to resell? If so, a2hosting.com semi-dedi ans reseller plans are very much alike, reseller features are present in both packages. It's just that on the reseller plan you/your clients get more traffic, and of course, the cost is different.

I think you'd be better to start from a reseller account from A2hosting.com. Semi-dedi doesn't offer so many features as a reseller one.