[eluser]Toppy[/eluser]
I would go with CI. My reasoning:
- CodeIgniter License: The unrestrictive licensing allows you freedom to do basically what you wish with your completed code and and the supporting CI libraries that will be required to run it. Further, if the code is released this provides a larger audience/target market.
- Support and Community: There's a lot of great and free support on CI. Your project may benefit from this and vice-versa for the CI community.
- Flexibility: With the reports that ExpressionEngine will be moving towards code that is based more on CI it would be easier to port it to EE in the future (as opposed to the other way around).