A VPS account gives the client more control than they would have with a shared account, since they can configure their own desired server area (with some limitations). It also lowers the likelihood of poor site performance due to demands on machines from other clients' sites. However, VPS hosting provides nowhere near the resources available with dedicated servers, somewhat less secure, and does not allow root client access to actually manage the setup and operation of the box.
VPS hosting usually costs a lot less than dedicated hosting, because clients get much less. This is often seen as a stepping stone between a simple shared hosting account and a full dedicated server. Like any hosting decision, the first step is to narrow down the possibility by checking the performance and reputation of the provider you are considering, either by talking to other business professionals who have their hosting company responsibility or by checking online honest reviews (on web board hosting or site devoted to web host monitoring performance).
Next, you must decide whether you want to be successful or unmanaged hosting; pros and cons have been discussed above, but this is usually a simple decision, based on whether you have the ability and desire to handle server administration. If you decide on managed hosting, look for reviews on companies' technical support capabilities while you're checking their reputation.
It's then time to assess your server's requirements: the power of the processor, the amount of RAM and how much storage you'll need, as well as how much bandwidth you'll be inclined to consume. It will depend on the type of site (s) you are running; the more complicated the site (if they provide a lot of multi-media files, if there are a large number of visitors, if they serve the page dynamically or run demanding scripts) that more power and bandwidth you need. You can then compare the dedicated hosting plans and prices of the providers you have on your list to make your decision.