D&D 5E - Monk with Q-Staff -- why not?
Their bonus action is an unarmed attack.
This, the main attack can be with a monk weapon but the bonus action attack is an unarmed strike.
At levels 1-2 yes a staff is the most optimal choice, at 3rd you probably want a hand free to catch incoming missile weapons and throw them back by spending a ki point, some DM's (I wouldn't letting go of the staff with one hand is a no action to me) might want you to have not attacked using a two hands on the staff during the round.
At levels 11+ it doesn't matter because all your weapons are doing base damage d8 thanks to martial arts.
Other reasons you might want to use different weapons would be different damage types against some monsters, and the ability to throw the weapon. In fact I take back the whole staff is the most optimal weapon, the spear is. It does a different damage type, can be used versatile for a d8 just like the staff, and can be thrown.
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