No way to tell with info given. Check the existing chainline and how far your inner chainwheel is from the frame, as well as how much adjustment is left on the front derailleur. That will tell you which way to go or if neither is satisfactory. Sheldon Brown discusses chainline in detail. The chainline can be adjusted to the right with a spacer but you need to look at where that puts your left crank, how far in the left cup needs to go and if you are losing significant thread engagement on the right.