This comes down to personal preference, but you should ideally try and make it balanced. If your lobby has 10 players, then you'd want fewer tasks than if you have 15 players, as there are likely to be fewer rounds. Similarly, it becomes rather unfair on the Impostors if you have visual tasks on with more than 10 players. In regards to the task bar settings, Meetings is usually the most balanced setting regardless of the number of players in the lobby.