What can I say here, Scratch is formidable box stock, turns into a legit beat with base upgrades, and either path is just icing on the cake.

I think most people would benefit from the Ruby Path, especially newcomers to the series.  You bump up the Critical Hit Chance, have a nice claw-roll combo on the primary side, and the Ruby Mask impacts a larger area.

That said, I personally prefer Sapphire.  Why?  I am not big on the "increase Critical Hit" upgrades and I am HUGE on Speed, or Armor.  Sapphire Slash is a cool, air based attack, but honestly I think the base upgraded tertiary still takes the cake.  Sapphire Mask slows enemies and while I'd rather have the increased damage of the Ruby Mask, it plays in well with your speed increase and vortex abilities.

Bottom line with Scratch, you really can't go wrong with either path...I think for the vast majority Ruby will be preferred.  Keep the aesthetics in mind too when making your choice.