100. Assuming youre a good player or improving player then you should be one of the better ones at the table and more money you could potentially win the better.
Also the more money in yours and the villains stacks, the more skill comes into play rather than a short stack luckbox shove fest.
if you dont want to lose alot id say buy in for the min amount, or a little higher. when i play with less money i feel more comfortble playing and not too worried about if im going to get sucked out on and lose a big pot.
100bb is the most used amount, though some people prefer playing with larger stacks, the larger the stack the more skillful you need to be! if you are a beginner though i'd definitely stick with the 100bb!