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If I compare both of these moba games, I would say for casual game and a better learning curve you should go for League of Legends.
Dota 2 is in my opinion kinda hard to get into. It's not very beginner friendly. And the game requires you a lot of micromanagement since it's possible to deny minions which is very unique compared to LoL.
The lineups can be also a bit complex, since there are a lot of roles you can choose.
Also be prepared to get flamed in Dota 2 and trolled. It's even worse than LoL
