I personally liked Emerald's frontier more. There were more facilities, they were harder, much more fun, etc. platinum's frontier sucked. I never even got any badges in platinums. I got all silver in emerald and two gold I think.
I havn't played my Platinum in a few months, but I will start playing again for these. I loved Johto, and I'm so happy that they have finally re-made these awesome games. Amen.