Most hobbyists use a 4 or 5 stage system. Generally the only difference between a 4 and a 5 is that a 4 stage has one sediment stage, a 5 stage has two.
You want a sediment stage, a carbon stage, an RO stage, and a DI stage. Pretty much every RO/DI system that is 4 stages has these. Brand wise there is not a whole lot of difference. I have a Kent Maxxima and an air-water-ice typhoon , both work great.