Sonic Unleashed

In Chan-nan next to an hour glass and day time stage is a line of rings to light dash on to nab an extra life. Stand on the side of the first two rings and face the wall. Press X to boost and the 2 rings will follow. This will glitch the rings respawn rate. A ring will always be present even if you can't see it. Just wiggle the thumb stick where the rings spawn and you will constantly pick up rings. Earn as much as you want and then head to Spagonia. Buy 99 chili dogs from the shop and eat them all. Each dog is worth 30 exp. Rinse and repeat and you can net tons of exp off food alone. 30 exp is the highest store bought food can get. Wentos has some food worth 50 exp and a hot dog vendor hot dog is worth 70 exp.

I got my achievement in no time this way.

or do windmill isle act 2 picking up about 400+ rings a time (most i had is 476) in about 2-3 mins go to the holoska and buy the jelly 30 rings each but gives 20 exp so for each run you can get atleast 260exp + about a bar from the dash and homing attacks on the way

To get the required rings i took the following steps:

1. Find Wentos and 99 buy chocolate bars for 50 and sell them back to him for 100 and repeat untill desired.
2. Go to Mazuri and buy 99 strawberry cake for 60 (30 exp/each) and 99 chili dog for 50 (30 exp/each).
3. Repeat the process untill you have the required exp.

Note: Wentos does not always have chocolate bars on him and he does move after you talk/purchase from him. He also does not always give you a profit for chocolate bars, sometimes he will try to buy them for less than what you pay for them.