Spark plug Denso or OEM Mazda

I would recommend that if you get one do a full service fluid change on everything. Change the coolant, the trans fluid, diff fluid, oil (10w30 or 10w40, do NOT use the 5w20 reccomended). You'll also want to set aside $80-90 for new spark plugs, and upgrade the coil packs to LS coils from Bennet Built whenever you can. Coils need to be replaced about every 30k miles.

Denso work quite well

The plugs EQT recommends are compatible. I’ve been running Denso 5749 plugs for over 10k without issue

i just put the densos in my '17 alltrack with a stage 1 tune and they run noticeably smoother than stock. i gapped them to 0.026" before install. it didn't seem like plugs would be that important for a stage 1 tune so i've been surprised.

Denso always.

I also went with the IKBH20TTs. I noticed my mpg was better after doing so, and the truck seemed to idle and drive smoother.

I ended up going with the Denso IKBH20TT because I couldn’t find any FK20HBR8 at a reasonable price and availability.

I replaced the plugs with DENSO 5358 roughly 10K miles ago.

I tried Denso once and didn't have great luck with them.

I tried one of the economy plugs on my 02 Accord. Ended up having to chuck it and buy a Denso.