Mechanically speaking what makes a item more useful, a raw bonus or advantage? [duplicate]

I’m looking at D&D 5e to homebrew a specific item and I’m debating what would be better. Advantage or raw bonus. The item is a coin that you toss it before a ability check or a attack roll. If the coin lands on the heads, you gain a boon. If the coin lands on the tails, you get a penalty.

I was considering making the boon a raw bonus of +3 to the subsequent roll if it’s a boon or -3 if it is a penalty. But it was brought to my attention that giving advantage/disadvantage could potentially be more balanced. So here’s my question, what would be better mechanically for the player?