This is kind of a surreal thread. There's a lot of bad info in here.
First, some clarification. A dedicated server is an actual physical machine that you have total control over (that desktop sitting at home could be a dedicated server, for example). The provider loads the OS for you (and perhaps a control panel if you've purchased one), plugs it in to power and the Internet and then walks away.
A VPS (Virtual Private Server also known as a virtual server, or virtual dedicated server), is...as the word 'virtual' implies...not a real machine. It is a separate environment on a dedicated machine that looks and acts like a dedicated box. The main difference is that there are typically lots of VPSes on a single dedicated server and all of those VPSes are sharing the RAM, disk, and CPU power of the dedicated box. If you've ever had the opportunity to play with VMWare then you'll be familiar with a VPS. Same thing.
So, now onto my points:
@bandboy: Comparing a dedicated and VPS makes perfect sense. They are both represented as being generally equivalent by most providers, yet VPSes are generally quite a bit cheaper. Comparing the benefits and drawbacks of each makes sense.
Comparing a VPS and a reseller is what makes no sense. 'Reseller' is a type of account granted to you by a provider where you are allowed to further subdivide whatever resources you've been given for resale to others. A VPS, by contrast, is a server configuration. A 'reseller' account can be provisioned on a dedicated server, a VPS, or even a shared web hosting account. The two are not mutually exclusive and have no comparison points.
@Mabus: Clustering VPSes cannot do the same things as a single dedicated. A single dedicated server has access too 100% of its CPU, RAM, and disk space at any given time. A VPS does not (unless it is a single VPS that has been allocated all of the resources of the dedicated box it is running on....and then, what's the point of the VPS?).
I'm curious what tasks you would cluster amongst VPSes, anyhow?
@Tailaa: You recommend a dedicated over a VPS because "as it has a lot of user options and it can also be managed through the service provider". You are probably referring to a control panel of some sort which can be installed just as easily on a dedicated box as in a VPS. The presence of options or management is not a function of the server configuration, it is a function of what your provider gives you.
So back to the original poster's question:
You mention that you want to sell web hosting. That's what I do and, I wouldn't run a VPS for any of my production servers. They're all dedicated boxes simply because I need lots of disk space and I need to know I have all of the CPU power. If one of my boxes gets slow, I know I can look at the resources and upgrade whatever it is that's slowing it down. If I'm running a VPS, I may not have the option to upgrade the CPU slice or disk space or RAM because those resources may already have been committed to other VPSes on the server.
Disk space it a big issue for me, too. You'll notice that move VPS plans have less than 40GB of disk space whereas even the cheapest dedicated box usually starts at 80GB. A server with only 50-80GB of disk space is useless to me.