Suppose you plan to drink plenty of juice--several times a day. You want both fruit and vegetable juice, including wheatgrass. You want high quality juice, and you don't want to spend much money on a juicer. Both the Omega VRT330HD and the Omega 8006 can do what you need. Which is better?
First, either machine will meet your demands. Both are slow-speed juicers with records of high durability. Both juice all kinds of produce, with particularly excellent records with the tricky greens and wheatgrass. Either would be an excellent choice based on those concerns.
So, how should you choose? Think hard about some issues beyond what you want to juice and how much you are willing to pay.
How much is your time worth? The Omega 8006 is more than two times as fast in juicing a pound of carrots as the Omega VRT330HD. This seems to be as a result of the way the horizontal position is aided by gravity, while the vertical styles fight gravity. Both models clean up much faster than the high-speed machines, but the 8006 may be cleaned up in as little as 30 seconds, by one report. The 330HD had no report less than 3 minutes.
How much do you value efficiency? The faster juicing of the 8006 leaves behind roughly 15% more juice in the pulp than the 330HD. Nevertheless, you can re-juice the pulp twice more and procure a little more than that 15 % out in about the time the VRT330HD took initially.
How high is your "goo tolerance factor"? Handling the pulp repeatedly may be less-than-appealing, if your "goo tolerance factor" is low.
How attractive does the machine need to be? The Omega 8006 is chrome--will that go with all your stainless steel kitchen appliances, or does the white/clear combination match better? Omega 8004 has the same machinery as the 8006, but comes in white. The Omega 8006 is a commercial machine--and looks it. The VRT330HD is made to be a kitchen appliance.
How much space you have: the VRT series are, well, vertical, single-auger masticating juicers. Their footprint on your counter top is approximately 7"x9" (but may not fit vertically under low cabinets). The 8000 series are horizontal single-auger masticating juicers and their footprint is at least double that of the Omega VRT 330 HD, but they will fit underneath any overhead cabinet.
How long do you plan to keep the machine? The OMEGA J8006 carries a 15-year warranty, while the Omega VRT 330HD warranty is ten years. (Both are pretty impressive in this age of "30 day" warranties being mentioned with pride by some sellers.) If you like new things often, the difference most likely will not matter.
The decision is rather like deciding on the "best" horse on the carousel--they have ups and downs, but essentially the Omega 8006 and Omega VRT 330HD are good solid work horses on the juicing circuit that will deliver you a great ride. The only differences are essentially an issue of your own inclinations.