Ballscrews are by far the better choice but they need careful selection and fitting. Rack & pinion is often used on large machines but there is quite a bit more work involved because it needs a gearbox or ratio applied using timing belts n pulleys, also more maintenance required.
Belts work well for lightweight machines but not so good for heavy gantry machines, they also require correct type and size plus tensioning system. I wouldn't use it for an 8x4 machine but I would on a smaller machine.

However, If you have never built a CNC machine before then I strongly suggest you re-think the size and build something smaller to learn on before attempting an 8x4 machine.!! . . . It's a mistake to think it's the same only on a bigger scale. Many builders have done this and failed or at best they build a machine that sadly leaves them disappointed. Then they try to correct the errors which end up costing them more money, but often they would have been better scrapping it and starting again because can't make a silk purse out of sows ear.!