The two are not a slow version and a fast version of the same thing. They are different jobs, and the question that settles it is not how much traffic you expect but how much of the machine you want to be responsible for.
Shared hosting: an account on a server we run
You get a cPanel account. The operating system, the web server, the mail stack and the control panel are installed, patched and monitored on our side. You upload a site, point a domain at it, create mailboxes and pick a PHP version, and nothing below that reaches you.
What you do not get is root. A custom daemon, a message queue, a system service or a package we have not installed is not something a shared account can run, and that is the real ceiling rather than the disk allowance. Our WEB-HOST plans carry one website each, from 1 GB to 4 GB of NVMe, with 2 processor cores and 2 GB of memory; the Business plans carry five, fifteen or forty sites on one account.
A VPS: the machine, and the administration with it
A KVM virtual server gives you its own kernel rather than a slice of someone else's. You choose the operating system at the order screen, hold the root password, install what you like and reinstall the whole thing from the client area when you want to start again. Our Istanbul plans run from 1 vCPU and 2 GB of memory with a 10 Gbit/s port.
The administration comes with it. Patching, firewalling, monitoring and backups are yours from the first login. That is the freedom and the catch in one sentence, and it is worth being plain that an unmanaged server you never update is less safe than a shared account somebody else is patching.
Which one, by what you are doing
- A WordPress site, a shop, a brochure site, a portfolio. Shared hosting, almost always. These are the sites cPanel and LiteSpeed exist for.
- Several sites that are all yours. Still shared: a Business plan holds five to forty on one account with one login and one renewal date.
- An application with its own runtime, a background worker, a queue, a database you need to configure. A VPS. The moment you need to edit a config file that is not inside your account, the account is the wrong shape.
- Something you want to be able to break and rebuild. A VPS. Reinstalling costs you time and nothing else.
What it costs to be wrong
Choosing shared when you needed a server wastes the time you spend discovering the limit. Choosing a server when shared would have done costs you the administration for as long as you keep it, which is the more expensive mistake of the two and the less obvious one.
Moving up later is not dramatic either way. An upgrade inside the shared range keeps the same cPanel account on the same server, so files, databases and mailboxes stay where they are. Moving from shared to a VPS is a migration, and it is a support ticket rather than a button.