obviously important is which organisation is going to give you a good course,
I did mine with an old navy boy, who was very demanding and ran a hard course. at the time I would have liked an easier ride but having come through it, I know that it was good for my character building, and improved my confidence etc, previously I was a self fly hirer at the same organisation and then went on to instruct and do commercial work at the same organisation.
other factors to consider
1) which organisation have you spent a lot of money with so far? as they will have more loyalty towards you, and are more likely to give you work once you have the rating
2)where would you like to work after the course?, as the company you do the instructor course with are more likely to give you work than someone they dont know.
3)if you spend a lot of money at one company on PPL, CPL etc, then go on to do your FI course at a second company and then try to find work at a third company, you have stacked things against yourself a bit.
hope this helps