I completely agree the ICFP contest matches real-world problems better. I can't recommend it enough. The longer timeframe requires discipline and good planning, while also providing a bit of a buffer for early (minor) mistakes.

Having a strong and well organized team is huge. You'll learn a lot about your teammates in the process, both behaviorally and technically. However, I've had to go solo the last two years and still enjoyed it immensely - it just changes how you prioritize some of the development.