[BoomerD]

In my experience, there's not a lot of difference between the units sold by most of the reputable sellers. They all are basically resellers. Some do assemble their units from components chosen for whatever reason, (cost, quality, performance, etc.) but still use essentially the same parts from the same group of manufacturers as everyone else. ( a Dow 50 gpd TFC membrane is the same, no matter who sells it.)
To me, the BIGGEST difference is in their customer support AFTER the sale.
YES, there are some companies out there that do a better job, or choose superior components, (Spectrapure is the first that comes to mind for me) and there are certainly some less than great companies as well, (NOT going to mention names) but overall, they all pretty much sell the same stuff...Shop by GPD, types of filtration, (you want Deionization, sediment and carbon filters) and by the reputation of the seller, and you should do fine. I've heard nothing but good about The Filter Guys, and woudn't hesitate to buy from them.