Thin clients are hardware terminals with minimal storage and applications. Zero clients don’t include local storage, they connect to a host server. It is also possible using traditional PCs and laptops as thin clients, installing a software which creates a remote desktop environment. HTML5 clients are hosted on a server instead of locally on a device and provide remote access through a web browser.
Using PCs may be expensive to manage, because IT department has to mantain and update them. Thin and zero clients may be cheaper, but require an initial investment.
Analyzing price and performance, the best option would be HTML5 clients, since they allow access nearly anywhere, you may even access virtual desktops from monitors, TVs or projectors connected to Internet.