Both GA CFI and part 135 turbine experience will make you a better pilot, in different ways. So the answer is both. You already have some CFI time.
The regionals will not care in the slightest where you got your time, but 135 turbine experience will give you slight leg up in 121 training (complexity, procedures).
If you're intending that airlines will be your career and primary source of income, I'll give you some advice... seek the fastest path that you can tolerate to your major airline job. Especially if you're going to need the income. Seniority is everything.