if you are buildiing from scratch, go with vortech. the initial cost will end up about the same, but the long term cost (electricity usage mainly) advantage goes to vortech.
I got a used tank with closed loop, but had to replumb all the closed loop pipes and get a enw pump, etc. I also tried the vortech route (that is why I know, at least in my case, the initial cost comes to about the same), but decided to just go with closed loop. had the tank I got not have holes for closed loop, I'll probably end up using vortech.