I am debating which micro-controller to use for a new open source hardware project. Spec wise, I would rather use an ARM Cortex M3, which is at a similar price-point to an Arduino(avr) based solution but with more processing power/peripherals. The only concern I have going with ARM based hardware is I don't want to lose potential contributors/developers who might be put off by working with ARM. Or competition wise--someone reproducing the project but with an arduino instead(e.g. Ardupilot overtaking Paparazzi)
I realize there is no straightforward answer to this question but I would like to hear your thoughts on the topic, and what other factors you think might weigh more on the success of the project.