Spark plug Champion 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.

Stick with Champion plugs in the 4.0L inline 6. Anything else will have you chasing a “stumbling” idle.

I use champion on my 04. No issues. The more expensive ones that’s when the issues start

I use Champion in my 02. Never had any issues.

I’ve been running champion plugs for about 40k mi without issue.

I used champion spark plugs.. no problems here

That price at 63.5k miles isn't bad imo. I spent roughly that same amount for my 2017 back in 2019 with around 40k miles (64k km). What's the service history look like? Have spark plugs been replaced, belts checked, engine oil changed at least 10-12 times by now? How are the pads and rotors?

I quit buying Champions 40 years ago for shitty quality.

Champion is garbage.

Champion aren't a great brand. They may have been at one point, but not any more.