I used to heavily use Coin Magnet, but ever since they patched the insta-reload glitch I stopped using it. I've only used the Score Bonus when going for the highscore objectives. Shield... is pretty useless, and Boost is nice but not necessarily rewarding.
As of now I'm using the Coin Bonus. It seems more beneficial than the Magnet in the long run since that can't be spammed anymore. But as soon as I buy out everything I'll probably switch to Boost for any runs played after that. But I have no desire to actually get to level 9.
Lol @ Gem Bonus, I'm never gonna reach that. Infinirunner? No thank you.