Try to do an octave on a piano with both hands and if you can't, then go with Violin or Guitar
Piano. In my opinion, the piano is one of the most beautiful instruments and also the most elegant. Few other instruments can get away with solos like the piano can. So much beautiful music you can play on one too, whether you're experienced or not.
Violin and guitar. AT THE SAME TIME.
I play tuba and I would suggest going with a low brass/low woodwinds instrument. Most low instruments don't play very fast music and its easier.