As a tuggy, flown a few different type's over the years - chipmunk(with converted lycoming 180 horse power), pawnee, super cub and robin DR400. By far the best tool for the job was the pawnee. The nicest to fly however certainly go's to the chippie. Such a fun aeroplane.
I would suspect the turboprop Porter or perhaps the big radial Wilga may be a force to reckon with though.
As a slight aside, the 'beefed up' grob 109 motor glider is no slouch either. We trialled one recently and it would certainly give the chippie a run for its money.
As for thermalling on tow - making use of any extra energy is always a boost...especially if the club charges 'per minute on tow' rather than by 'height'. If the glider pilot is willing to crank the bank...then all the better!!