Groudon vs Ho-oh. Which is the best to power up?

The 1-2 ton Groudon smashed everything.

What movesets are you planning on having when they are powered up? What are your intended uses?

I powered up my best Ho-oh (sw/solarbeam), and am pretty happy with it as a gym attacker. I did that right before Groudon became available. I think Ho-oh's high defense stat allows it to be beat-down king. I think Groudon might clear mon from the gym a bit faster, but not survive as long. I'm sure there are purposes for which Groudon would be better, but I don't regret powering Ho-oh, and don't need another generalist, at the moment.

I powered up my only Ho-Oh because it has Extrasensory/Brave Bird and I needed something to help me beat Machamp raid bosses with Dynamic Punch and Heavy Slam. No regrets. Thanks to that, I can defeat any Machamp and earn rare candies and TMs.

Groudon with Mudshot and Solar Beam, however, is a weapon of mass destruction where I live because we have clear weather over 90% of the time. The +36 boost that Solar Beam gets from clear weather takes an already devastating move and makes it truly OP. It's fun watching a 3000 CP Blissey's health bar lose a huge chunk after one Solar Beam hit.

So it depends on your needs. If, like me, you missed out on Lugia and only have one Dragonite with Hurricane, Ho-Oh can help you succeed in every Machamp raid regardless of moveset. If you want a bulky attacker who hits like a truck, Groudon. I definitely think Groudon has more uses, but I'm thankful to have powered up the Ho-Oh because that investment has paid for itself in rare candies. I hope that helps.