It’s up to you, it’s your stag party.
I’ve been on both types. Large ones are a good laugh as you meet people you haven’t seen in a while and you don’t often get a chance to go away with. Having 30+ people staying in the lakes with drinking, eating, walking, go karts etc. was great fun. But there was plenty of faff.
I went on one last year for a very good friend and it was small. His brothers and a few good mates. We mostly had a really chilled day and evening (he doesn’t drink so no wild nights on the town). Nice meal, went to a comedy club a few bars. Really enjoyed it, good banter with genuine close friends.
Large ones you are limited to what you can do, they can get out of hand and become something you don’t want depending on the group, especially if they don’t know you well. Small ones with close friends will be more personal maybe quiter but equally fun.