Don't obsess and spend weeks/months investigating what is the best game to buy as first game and focus on only getting that one specific game.
It isn't that important.
It's not permanent (although many keep their first game), it won't stay with one game, if you're really bored you can sell it and get another, ..
Just get a fun game, have an open mind (dozens of games are fun for you, especially if you don't know them all well)
Make sure it's in good condition and the price is reasonable.