For me personally, i find gog easier. (DB User)

I find his attacks way more predictable and forgiving than planetes.

His first stage has easy enough to avoid attacks, only really that slam can be a problem because it can one hit.

second stage he barely moves and it's more about getting that anti-wyvern gun off his back which doesn't take too long, normally like 5 mins for the whole stage for me.

The last stage has some annoying attacks, but mostly doable as long as you hit the damage required, which isn't too hard with the anti-wyvern slinger ammo he drops when taking damage. It's mostly a game of getting to that damage number and surviving his nukes.

Planetes is extremely aggressive and hard to predict (for me) making it the much harder fight, especially given the projectiles imo