I bought my RO/DI system from Bulk Reef Supply (forum sponsor). It is the 75 GPD Stage 5+. I rent for now, so portability is important to me. That set up is great. I can store it beneath my bathroom sink, and when I want to use it, I just unscrew the aerator on the sink, and screw the RO/DI system in. I did need to buy a $5 adapter from Home Depot though, but that's no big deal.
Make sure you go to the Bulk Reef Supply sponsor forum on this website and join a group buy if you choose that one - you get about 10% off!