Pick one and stick to it. Inside big openings like the Spanish and the Queen's Gambit Declined you have various options, you can switch from one line to another if needed.
However, in some cases, you need to have both a solid and a sharp opening in your repertoire so you can adjust to circumstances (on this specific day you're bored with dull positions/you're facing a maniac/you need to play for a win). Moreso with black.
Also, in the long run, you need to expand your repertoire little by little and try new things from time to time (to improve as a player the number of positions you can play and to avoid routine).
1) As White, in e4 e5 openings, is it better to learn the Scotch, Italian, and Ruy, or to pick one and study it like crazy?
2) As black, in d4 d5 openings, is it better to learn both the QGA and QGD, or to pick one and master it?
What’s your approach?