I have a Village Marine and it freaks me out because it is a VERY PRICEY unit, and it was given to me but I have to keep it because it seems bulletproof and the factory support is the best I have experienced anywhere for practically any product. Don't get me wrong, some other companies MATCH the support, but none are better. Anyway, back on point.
Research the support and reliability of each unit, as well as the ease of maintanance. The best gal/$ is nothing if the unit breaks down or is so hard to flush and bio after each use that you let it slip and ruin the membrane. Gallons per dollar doesn't speak to whether or not the unit WORKS FOR YOU, which is the single truly important issue. Well, some people are also very concerned about space consumption as well, which is also valid.
One last thing - the most you might get here is discussion and a bit of experience - you will probably have to do your homework in more forums than this.