Getting your CFI without the restriction of the sport pilot would be best for most. At a local flight school that does training for sport pilot and private pilot they feel that less than 250 hours is not sufficient to teach anyone. They will take a new CFI but they are sent out on structured flights to the syllabus. There is a lot of oversight and plenty of experienced CFIs to help out, in particular with stage checks and end of course checks.
I get that you can be a good teacher already without needing to be a pilot and that the mere number of hours don't really mean everything. I can say that I'd be reluctant to take training from a sport pilot CFI with 150 hours. Again, I'm not sure how much better they would be with an instrument rating, commercial pilot certificate and 250 hours but it is almost double the experience. In the right place, like when I was the chief pilot of a 141 school we could take 250 hour CFIs all day long, because the CFIs weren't making decisions on training just doing the lesson per the standards and syllabus. All ground training was done by ground instructors who were also CFIs with a lot of experience, so the low time CFI just needed to make a steep turn look like a steep turn and so on. All of the order of lessons, stage checks, supervision etc. was done by senior members of the school. All of those guys had thousands of hours and had trained and recommended many pilots.
If you can swing it, do the CFI. You will have taken two more checkrides and have at least 100 hours more experience. They you can really look at working anywhere without restriction.
- Mike Shiflett