The only games where I actually went to the Game Corner in was FRLG and HGSS. I personally prefer Voltorb Flip, since it's not completely up to luck. A while ago while I was waiting for Baoba to call me for the Safari Zone blocks in HG, I spent ~2 hours playing Voltorb Flip. I can't remember how many coins I earned (probably a small amount) but I remember getting to Level 4... I never said I was good ;P
Slot machines suck. Although, it does make me happy when I get three 7s!
I might try the roulette in RSE once I feel like playing Gen III again.