R2D2 mods: offense or health/protection?

I'd be inclined to say there isn't a right answer to that question without actually putting a few different sets on and testing how the matches play out with your own squad in arena.

If you mod for HP and find you are not killing them fast enough or leaving them with a sliver of health left switch to offense. If you mod for offense and are dying off too early switch to HP.

Health would allow you some flexibility to use him on a Padme squad in place of ahsoka too though. Can be useful there against DR teams with marauder or malak faster than DR especially.

As an aside I use L3 and Nest with CLS trio when on defense. That makes a mirror more difficult and lets you use R2 with JTR or Padme on offense. I find JTR really needs R2 to be useful these days. Although with ships reducing the number of character teams in this GAC I've found a JTR team isn't really needed at all.