The first one is a masterpiece and is #1 on my list. With the first episode, I could tell I won't be disappointed.
Steins;Gate 0 really isn't a prequel as its timeline is between episode 1-23b and 1 through 24. I recommend watching Steins;Gate TV series, Egoistic Poriomania, and Load Region of Déjà Vu, plus episode 23b. At a minimum, (re)watching Steins;Gate TV episodes 1 through 22 plus 23b