I have the Intelliflo VS model as my main pool pump and love it. The only difference between the VF and VS model Intelliflo's are in the variable controller that is mounted on the base pump. The physical pump itself is identical and despite what you may hear, the pumps have identical spec's because they are exactly the same. In fact, a VS can be converted to a VF and vice versa simply by changing the control unit on top of the pump.
[attachment=2:2717xfu4]Main Pump.JPG[/attachment:2717xfu4]
The difference is in the controller. The VS is a variable speed pump and the VF is a variable flow pump. This is really just two ways to get to the same thing but there are some basics benefits to each that must be matched to your pool.
On the VS (variable speed) pump, you can change the speed of the pump but you cannot directly control the amount of flow (GPM) that you get. You have to guess at the flow. In fact, without the Easytouch or Intellitouch Controller, you really don't even know what the speed is, you can just change the speed up or down until you find a speed that works. Its really just by feel. If you have one of the contollers, you can actually set the speed you want in RPM's and it will control the pump for you. Also, by itself, you can have 4 preset speeds on the VS pump. With one of the Pentair controllers, you can preset 8 speeds, which should be plenty. Over time, as your filter gets dirty, you will slowly get less flow (GPM) with the same pump speed setting. Since the speed stays the same, your watt usage stays the same. Below is the control panel on the VS pump.
[attachment=0:2717xfu4]VS Control Panel.JPG[/attachment:2717xfu4]
On the VF (Variable Flow) pump, you can set what flow rate you want and the pump will automatically adjust the speed to match this flow. The advantage is that as you filter gets dirty, the pump will automatically start raising its speed to keep the flow constant. However, as the speed increases, so does the watts used, which equates to dollars. Below is the contol panel on the VF pump.
[attachment=1:2717xfu4]VF Control Panel.JPG[/attachment:2717xfu4]
IMO, two of the main factors to help you determine which of these pumps is right for you is 1 - whether you have a Pentair Easytouch or Intellitouch controller and 2 - whether you have an infloor cleaning system. Without one of the Pentair controllers, or maybe another 3rd party controller, you really have to rely on the pump controller to change settings. The VF has a screen which gives you information and it has many more control options. The VS has an up and down button for speed but you don't know what the speed is. If you have one of the Pentair controllers, most of that advantage is taken away since you can control either pump just fine from the Pentair Controller. I have the EasyTouch and it works great. Since I never go to the pump itself to make adjustments, I don't notice the difference between the VS and VF interfaces.
The other issue is regarding an infloor cleaning system. Since the VF pump adjusts itself by monitoring flowrate, it doesn't work as well with the infloor system. Since the flow rate is changing a lot, the pump would be constantly changing speeds to try to keep the flow rate the same. The VS does a better job, because it just stays on the same speed regardless of an pressure or flowrate changes.
The main reason I bught this pump was for efficiency and to save money on my monthly electrical bill. One of the things I really find interesting is using my EasyTouch to monitor the watts used. For normal pool circulation, I run the pump at 1,800 RPM's which equates to about 450watts of power. In 10 hours I only use 4.5KW of power which is about 60cents a day. The cleaning system setting is at 2,400 RPM, which uses about 900watts of power and the SPA setting is at 3,300 RPM, which uses about 2,000 watts. At this rate, I think the payback for the pump will be about 16 months.
Let me know if you have any specific questions that I can help with.