Groudon Powerup

Shiny, because
a) its shiny.
b)its stats aren't that much worse if any.

Or if you prefer the regular Groudon look, then go with the regular one

Neither. What are you going to use them for in the short term?

Shiny, bit better defense. Do you need it right now?

I'd say the shiny, unless you dont like the shiny. the shiny also has better attack

Is this a subtle shiny flex thread? The answer should be obvious.

Shiny. Then give it Mud Shot and Fireblast, and when your Raiding Group for Palkia goes apoplectic, explain to them that "I don't have a good Aggron to power up.".

Warning: Be sure that you are standing at least 3m (10ft) away from any Hardcore Raider when you say this. Heads of hardcore PoGo Raiders have been recorded to explode with a radius of just below 10ft when discussing using Aggron in Raids, and brains take specialized laundry detergent to get out of clothing. (For this reason it is advisable to communicate this via Discord or other form of Chat program rather than face-to-face.)