Don't get me wrong- the first few years I watercooled, I only used the hardware store tubing. It worked, but it does get unsightly fairly quick, unless you run some kind of colored additive in your loop (which we usually discourage- dye is fairly safe vs. 'coolants')..even then, it stains pretty easily.
As time has gone on, there has been more demand for the colored, UV reactive and enthusiast grade tubing we see today. Some of it is ridiculously priced at around $3 a foot. Most brands are relatively good and there are some that are slightly different at flexing tight bends vs. others. I've used Tygon and Feser tubing for the most part with a slight preference for Tygon. I'm going to try my luck with PrimoChill in my current project, so I'll be able to tell how that works out.