Of course I need good support from VPS hosting provider. I used to read reviews on forums about hosting providers before buying a hosting package from them. I can test their service for 1 or 2 months to know their services are good or bad.
Yes RAM is the first point, because you will not have the same I/Os (writing/reading on the disk) than with a dedicated as you are not alone on the SSD.
So to get a fast webserver, store the maximum in memory !
I'm currently writing a thread to explain how using cache on a vps.
I think it also is what you intend to use the VPS for, Database driven? Public Site forums / user counts etc... But as with your personal computer, for the most part - More Ram and More CPU power cannot go wrong - and VirtuBox will be providing some good info on Caching which is another feature good for a busy VPS...