If it's "for teams", then users seems like a better option. You wouldn't want to punish usage. Remember, you are creating value and you want to make sure that the user gets as much value as possible... and that's by sharing more often, typically. And, as the user base within a company grows (hopefully), the price should go up. This stuff is always hard to figure out and I don't think most companies are always 100% happy with how they are charging, but if you are a team-based app where you can easily measure by employees using it, then user is probably the clear winner, even with the little information you've given.