100% mouse for me.

I can play causally even without headset But precise and comfy mouse is a must.

Love my DeathAdder V3 Pro, and it’s my main mouse since more than year.

I think its a gaming Mouse and a good quality headphone. 

It has to be an amazing monitor. I want to have an experience that is buttery smooth to look at. I also really like my Razer Leviathan V2 X, it has AMAZING sound quality for games with banger music.... like Halo and Doom

My Razer Basalisk V2 a old mouse yes, but a  great one at that and has stayed in near perfect condition since  I bought it years ago. I would not be able to survive without its customisability and sharp response rate. Might upgrade to Basalisk v3 tho but yeah/

Having the keyboard key letters light up really helps me quickly hit the keys I need!

A close second is the sensitivity increase/decrease on my Elite Deathadder when I’m swapping between weapons in shooters, being able to decrease for sniper rifles and then increase for twitchy spray and pray weapons really helps!

For me, the winner is definitely my old giant mousepad Goliathus Chroma Extended ... with its perfect surface and chroma lighting it makes the gaming experience much better. The fluidity of the mouse movements on its surface helps me enormously.
But, together with the Basilisk V3 X HyperSpeedv mouse correctly calibrated on this mousepad, with its perfect ergonomics, with silent and firm scrolling, buttons that don't move around, gaming becomes a real pleasure.
If I add the gaming keyboard along with the high quality sound of my old Kraken X Lite headphones with their 7.1 surround, everything becomes great!

EDIT: Double post disregard this one!

my razer deathadder

Mine is a tie between good monitor/display and a headset. But leaning more towards the monitor. 

My most important peripheral definitely is the gaming mouse. Ever since I bought the razer deathadder V3, I never use other mouse for my working setup.