As someone who went to the airlines from flying instruction, and who carried on instructing I would suggest that unless you have a passion for it you would be better served by the tug pilot role. The F.I. is a large investment with little return and there are too many instructors about that have no real interest in the job other than the hours, if you feel you have that real interest in passing on your knowledge then it's a challenging and rewarding role( not normally in the financial sense).