I'd like to be able to do both.
My guild is doing geo and we can get 7 stars, so the rewards are better than doing hoth.
But we get those 7 stars by fighting in the first phase and then basically by deploying for most of us. A few players can clear a round or 2 in the 2nd and third phase, but only in one or two battles.
I only have 2 teams that can really do anything after phase 1, so I'm finding the geo battle really boring. Just deploy and try to fill platoons.
At least I can battle on hoth, and the pve is the main reason I play this game. All the stuff I've built for hoth feels like it was a waste.
Like I say though, we get slightly better rewards, so geo it is.
If both were available, there is nothing forcing the people who don't want it to do it.
Rewards could be spread over both for guilds that selected to run both, maybe?
