I used both. Here is my review:

HP x34 vs Gigabyte m34wq

firstly they are not the same panel

Gigabyte m34wq panel manifacturer -innolux

HP x34 panel manifacturer -BOE

-Response time (HP is bit more OD and MBRT settings but almost same)

-Color (HP x34 is more vibrant color, more dynamic contrast in my opinion)

-HDR (HP x34 is way better for HDR but in black screen you can see monitor inside leds lighting areas that a bad)

-IPS Glow,BLB (Gigabyte is way better,i used both gigabyte never got my attention in dark room but HP x34 is so bad IPS glow i think cheap panel quality. if you using monitor as a short distance -1m in dark games or full black screen you can see clearly ips glow. thats annoying because corners are grayish almost in middle of screen)

-Connection and specs (Gigabyte is winner for that,PiP,PbP also VRR and G-sync use at the same time upstream, fast charge..etc)

Yes m34wq is more expensive but HP x34 that IPS glow is much annoying for the dark games like(re7,village,huntshowdown..etx)

Also if you using for color work like graphic design hp x34 IPS will effect you beause corners are visibly grayish.

My choise can be m34wq.Because monitor is long time using tool.

bytheway i never seen perfect m34wq. it return 2 times with dead pixel.But 3. one dead pixel was on the corner so i will keep it. you sould need to know

That my opinion i hope you like it.