Synthetics really do offer advantages, I wouldn't avoid them like that. Just don't change them as often or you're wasting money. Anyway don't forget about the power steering fluid & filter (yes, there's a filter in there).
diff fluid...... Mobil-1, Amsoil, or Red Line
trans fluid.... Mobil-1 ATF
brake fluid.... Valvoline SynPower (best bang for the buck) or ATE Super blue (even better, costs more though)
radiator fluid... Mercedes anti-freeze ONLY!
power steering... MB fluid, Mobil-1 ATF, or Valvoline SynPower (I used Valvoline)
I find that the tranny fluid & filter needs replacing by 25-30kmi, and I can usually feel a difference by 20-25kmi, and the improvement is very obvious when I do change it (that's with dino ATF, not synthetic - haven't reached the next change interval yet to switch to M1! Another 4kmi...