I have the option of either picking something fun to build with no real-world application (but uses cool technology that I want to use). Will have lots of passion this route
or
I have the option of building something that solves a transparent pain point with a group of talented engineers I enjoy solving problems with. Tech is not cutting edge, but it's fun and enjoyable to work with. Medium passion levels.
I was wondering what was the better marker ? Should one spend time solving problems -or- Should one spend time building personally interesting projects ?
If you want the former, go with the safe option that solves an obvious problem. If you want the latter, go with the fun option that uses the cool tech you want to play around with.
Then again, why is it a choice between one or the other? Could you find a problem to solve that the cool tech you want to use just happens to help you solve? If so, do that.
Once the fun is done, switch to the problem solving one.
A mix of fun and meaningful projects is ideal. Spend some time doing things just because you enjoy, and some time doing things because it makes life better for your community.
I am not you. But in your situation, I might be inclined to work on the group project that is needed, and do the "fun" project on the side, in spare time.