I respect but on the whole dislike Bachs keyboard music with the exception of that and other concerti for keyboard, however if it was a toss up between the Ravel and the Bach, the Ravel would win every time xD. Then again if it's obviously out of my league then I won't even try it and opt for the Bach
Okay, but now it's not really clear to me wether you've ever played a piano concert before or not. Did you? Because if not, I'd go for the Bach first to gain some experience. A suggestion to work to the greater romantic concerti (which I on the other hand mostly don't like too much). My teacher worked me trough it look this:
I began with her when I was 5 years old in 2004. After 3 years she said I was ready for Bach's BWV 1052. Before that I played the Bach Sonatas for Piano and Viola da Gamba, the Sonatas for Violin and Piano, and most of the Beethoven Sonatas for Violin/Piano and Cello/Piano.
So the BWV 1052 at age 8. Then at age 10 the Beethoven 2nd Piano Concerto and later that year also the 1st Piano Concerto. After that, at age 12 the 3rd Piano Concerto and at 13 the 4th Piano Concerto. Later at age 14 the 5th Piano Concerto (Emperor). I never really played Mozart too much, only the Piano Concerto Nos. 18, 20, 21, 24 and 27. Then in 2013, at age 14 she assigned the Schumann Concerto and Grieg Concerto. A year later at 15 I played the first movement of Brahms D minor concerto and later that year also both Chopin's Piano Concerti. And now (2015!) 16 years I recently played the Brahms D minor completely and also his 2nd Piano Concerto.
Besides that, also a lot of solo piano music. Maybe you could follow this guide roughly too. Because at the point you can play the Brahms D minor, you can surely also play the Ravel G major. It certainly worked for me.
BW,
Marijn