Ignore any advice based on the premise that there's a single right or best answer that applies to everyone. Some people and their play styles are better suited to 6max, others to FR.
Plus there's the enjoyment factor to consider. If, for example, you try both and find you enjoy FR more but have a higher win rate at 6max, it's completely fine to decide to play either, or a mix of both. As a recreational player, you don't have to maximize your EV.
In addition, 6max is not the only way to play more hands. You can also play more FR tables. There's often a kind of an implied assumption of playing equal numbers of tables at once. But there's nothing that says you have to.