Hey guys,
Can someone tell me which type(platinum, double platinum, iridium) and which brand of spark plugs is a good choice?

 

I'm not a Montero Sport owner, but you might try looking the information up in your FSM, your owners manuel (under specifications), or checking on the following site:

https://www.mitsubishiparts.com/oe_parts_catalog.html

My rig is a Montero and I use iridium tipped plugs only.
Although I use DENSO SK16PR-A11, I'm sure there are many other choices out there...

Good Luck

 

Try these from supersonic spark plugs I have had good luck with them.
their wed address is supersonicsparkplugs.com - supersonic spark plugs Resources and Information.. They are based in Denver. They will make a deal on the plugs what ever brand you buy. They slightly modify the plugs. its worth just talking tothe owner.