This is a difficult question,
I'm a massive fan of Fantasy, Action, Adventure Isekai anime so definitely has to be something like that. I'd say Log Horizon would be my choice.
I'm a massive fan of MMORPGs and the Classes/Sub-Classes are done amazingly there I feel.
Wow, what a tough question: Do i take the safe route and pick a slice of life and actually live, or a fantasy-themed world where i'd probably die but it would be amazing!? Hmm, I cant resist the possibility of a fantasy-world. So what if the risks are insane and how unrealistic it is, the chance to experience something like that, to get to fly or have a cool power outweighs the possibility of death, at least for where i currently stand in life: The World that i choose therefore would be the Kingdom Of Magnolia (FairyTail).
Hmm, if I could join Project D. Then I won't mind join the world of Initial D.
If I could be a Nakama of Luffy & join his Crew. I won't mind joining One Piece.
If I was struck in a OP MMO game. I won't mind joining SAO/Overlord (Don't have to be stuck but worlds like Log Horizon/Accel World would be epic too.
If I can keep eating every few minutes and gain muscle & get stronger. Then ofc. Toriko.
If I was a Sayajin race. Then I would join Dragonball.
If Jiraiya was my Sensei. Then I would join Naruto.
As u can see. All sekai can be awesome.
If you can be a part of it. :P
I would like to live in the anime world of Knights Of Sidonia as i would love the constant thrill of not knowing what would happen next and i would love to attempt to become one of the Garde pilots, Although i might die eventually i still think it would be worth it.