I need to build a desk / worktop / workbench for my retro computer projects. It will be used daily, so I want to have extreme durability to protect against wears, scuffs and scratches as much as possible. I have MDF cut to size, sealed and primed. What product type to consider for a top coat and why? Should I go with polyurethane, epoxy, latex, oil? Opaque black or white would be nice, but the priority is the durability. I'm UK based, I have experience with trade products of the brand with the big white dog.
You'll get similar life from polyurethane and oil paint. It might be wise to use a satin or matte sheen to reduce the appearance of wear, which is the real issue. You can always recoat if actual wear-through or other damage occurs, but you probably don't want it looking distressed immediately.
Epoxy might give a little more hardness and thickness, but it's not as easy to work with and may not end up as smooth initially.
You might consider having a piece of glass cut to fit your desk. 1/4" standard glass is actually fairly tough, especially if you were to put a layer of felt or similar underneath as a shock absorber. I used a piece on my desk for many years without issue. A nylon work mat over the top would virtually guarantee durability. Acrylic or polycarbonate sheet could also work, but it'll scratch and scuff easily. The latter is virtually indestructible.
Of course, you could always lay plastic laminate on it. That's fairly easy to do and would be nice and tough. You just need a router with a bevel, ogee, or straight bit to finish the exposed edge.
Honestly, the best option for a bench that expects hard use is a sheet of 1/8" "tempered hardboard" - I don't know if that's one of those places where we are separated by a common language or not. Masonite® is the best known brand name, though they make multiple products so that may not be definitive. You put a trim board sticking up 1/8" (or the thickness of the hardboard you can get, which might be in mm, of course) all around the edges of the benchtop, and the hardboard just drops into the recess (it lays flat very nicely, so it will stay put until you pry it out of there.)
When it's been scarred, burnt or otherwise damaged to the point that it offends, you flip it over for a whole new surface, and when that one offends, you replace the whole thing - the stuff is relatively inexpensive.
You can get it with one side melamine white - otherwise the color is a moderate dark brown, and for most workbench purposes I'd find the melamine a bit hard/slippery.