I wrote a blog post to answer that question. I did a lot of research and found that Cart Surfer is the best, but Pizza Tron 3000 and the surfing game at the cove are pretty close.

—
Beztar

play the sufeing game at the cove. when i played that game it got me over 80 coins!

I think the fastest two ways to make money are with Pizza Tron 3000 and Cart Surfer.

found this cheat on the internet and im goin 2 try it out now but loads of ppl says that it works
after playing the jet pack game or the pizzatron 3000 and uve just finnished press tab until a yellow box goes under or around the done or finnished then keep pressing space and ur coins will keep doubling

Well, you could cheat it instead, hehehe, basically just play it again and again. Practice makes perfect anyway.