Hmmm i'm thinking....... i reckon aluminium, has to be able to be locked in position and capable of taking some weight of the pole so at times it can be dragged along the bottom of the gutter. A waggly bit of pipe on it's own is no good - too knackering to try and hover the pole above the gutter. Pole angle and head angle will be important to work together and kept at the optimum angle for the whole clean. Difficult to change pole angle once you've started i think. Need a selection too.
Get my pop riveter out soon and source some pipe.