Okay as a Hyatt Diamond your treatment will certainly be better at the GH than as nobody at the IC, but the Club at the IC is very nice.

As a property, personally, I think the IC is well ahead of the GH. The GH could be in any warm, sunny place and is not very Balinese. It is very big, but I found it quite soulless and didn't like the beach much. Also location wise I prefer Jimbaran over Nusa Dua any day.

YMMV, but consider signing up for IHG Ambassador (the kit and free weekend night certificate likely won't arrive in time for your trip) getting a guaranteed one category upgrade. If you can spend the $$$ get a Club Duplex and Ambassador status and you should get a higher level suite, e.g. Balinese Suite or even better like Uluwatu or so.