In all honestly, the only thing that you can rely on is to find a good teacher that meets your needs in ANYTHING and start with that. If you have all good teachers, then it depends on your mindset. You will become the mind you train. So:
I think starting with a good aikido teacher --> meaning who has aiki skills and can deliver is the best way to start aikido.
I think starting with a good MMA teacher --> meaning who has aiki skills and can deliver is the best way to start MMA.
I think starting and staying with with good teachers in general --> meaning who have aiki skills and can deliver them to both aikido and MMA and knife fighting, etc, and in doing misogi training and learning about the spiritual principles that they are physically and mentally manifesting is the best of all. And my feelings wont be hurt if no one agrees. And my mind probably won't change much either. I'll call that aikido and you'll have to be a total bad-ass to convince me otherwise.
Rob