Ultra Deep Sea: Would be visually cool but kind of hard to breath, could absorb with Nihilego if you wanted and become fucking Yog-Sothoth

Ultra Jungle: Would probably be hot and humid, could chill out with Buzzwole though and get ripped, could live in the trees

Ultra Desert: Pyramids in the background are probably human-made so you could live there, or live with a tribe of mommy Pheremosas

Ultra Plant: You would probably need to wear some kind of special suit to protect you from the fuck-tonne of lightning strikes, but the scenery would still be really cool. Also it's probably cold with all the dark clouds and shit

Ultra Forest: Would probably be comfy, beautiful forest scenery where you could live in a house drinking tea.

Ultra Crater: Wouldn't be surprised if the air was slightly toxic, would probably need some kind of protection. Celesteelas probably fucking blasting off every now and then. If you catch a Celesteela you could ride on it though, like a spaceship.

Ultra Ruin: Basically Fallout/Mad Max/ but in Pokemon world. You would need to wear a special suit all the time which would get uncomfortable. Could roam across barren, toxic wasteland and would have to avoid Guzzlords and probably mutated, sickly scavengers/raiders. Food would probably be extremely scarce.

Ultra Megalopolis: Could have pale-skinned alien waifu, life would be made easier with technology, food is probably entirely manufactured due to no sunlight. You won't get melanoma.