Interesting how we all have different grinds. Mine has definitely become Gravity Switch (funny since it used to be impossible but is now the shortest and easiest to max for me), followed by Sky Jump. Cat Race is still the easiest game but takes too long, so I wait until 3rd if I even go that far. Bridges is actually fourth for me now because of how quick it is. I'm over Spirals which takes too long, too. I don't touch Line Breaker or Dancing Snake unless I have to. If I'm farming coins it's mainly just GS and SJ back and forth.
I use Chrome for Bridges, to answer a previous question. There's the occasional round where I never get into rhythm, but it's night and day with where it started. At the beginning I couldn't get two stars.