I've always bought my RODI units from The Filter Guys . I've always used: OCEAN REEF + 1 FIVE STAGE 75 GPD RO/DI . Here is a pic:
The Pros are that the water quality is great, filters are easy to change, and it is easy to hook-up.
The Cons are that I have flooded the basement with it several times (easily avoidable if I had made an auto shut-off or something like that, and doesn't really have to do with the unit itself)
The guys who work there are great and they will have your unit shipped in a few days.
I have used several different types over the years, but my favorite is the BRS 5 stage. I get great life from the membrane and I don't have to change the filters quite as often. It seems like they hold more than others.
I make a lot of water, so I upgraded to the 150gpd system and set it up to recycle the waste water. I have the booster pump as well, and my setup works flawlessly (knock on wood) The only problem I have had with it is I cut my TDS tester line accidentally. I can splice the line, but I figured a but connector might mess up the signal so I plan to buy a new "In" wire and redo it. The "Out line isn't connected so it still works just fine, and I can monitor it, and I have a handheld TDS to double check it.
It fills my rubbermade brute in just a few hours and meets all my water needs.
I also should note, that I don't use the Deionization filter. R/O water is already like a magnet ready to suck up atmospheric pollution. Deionize the molecules seems counter intuitive to keeping pure water pure. But then again I don't use my water right away. I don't need it sitting in an container pulling anything with an Ion out of the air just to regain molecular balance.... Also, I personally think it removes specific minerals that are better left in.
All in all, I love my BRS unit, and don't see myself changing anytime soon.