hi Tosh
A car mate
If you're planning on using a car, unless other forum members can advise otherwise; don't go for a trolley system. They're difficult to get out of a car; especially if you still carry ladders; which most WFP users still do.
One local window cleaner I know has to remove his ladders everytime he wants to get his trolley system out of his car; and he finds he uses far more water than me, even if we clean the same amount of properties.
If you plan on working from a car, get a Shurflo backpack; they're great for working out of a car.
However, with a backpack, I'd advise you to do 'tops only' (mostly unless it's Georgian or Leaded) and squeegie the ground floor stuff you can easily reach.
Also, there's another option; cheaper than a van (safer (apparantly) too); do a search here for
trailer WFP systems or use a trolley system with a trailer. Another local window cleaner used to do this before he purchased a van; still using the same trailer system.
But honestly, unless another member here has a good experience with working with a trolley system from a car, I'd strongly advise you to go down the backpack route.