Which projects do you participate in?
Other (Please Specify):
Arduino is a project but sparkfun is a company, not sure about the other 3, it sounds a bit like comparing apples and pears. The open nature of the last option can give you a dozen names that might be meaningless to you so how would you classify them. So the value of the answer is restricted in its use.
It would have started with some more quantitative questions:
1) do you participate in open source hardware. Y/N
2) do you participate in programming platform - robotic platform - ...
3) how many projects are you participating in
4) how many projects have you done
5) how many were succesful, why (your Q3..6)
6) do you participate on discussion forum (your Q2)
It is not 100% clear for me from the description what you want to learn or what insight you want to get (but that may be on purpose)