I think the choice of derailer is driven by the shifter. If doing a bar con in friction, probably either will work, as will many Shimano 3 spd F derailers, such as an Ulteggra or 105 triple. As well, mounting is needed to be considered, what is the dimensions of the seat tube, can those 2 derailers you mentioned be mounted on the frame, what are you clamping to and/or is it a derailer hanger.