Great cheatsheet for going on a raid
http://www.eurogamer.net/articles/2017-06-23-pokemon-go-type-chart-effectiveness-weaknesses
I'm no expert on type weakness or strength, so I printed this article this morning and took it on my first raid. The raid was a level 3 Arcanine, so I didn't need the list to tell me ground, rock, water. But, I am going to carry the list with me in case I run into some oddball that I can't remember what is best effective against it.
Answers
Trust me, i may do that to. i fought an Arcanine and i don't overthink it so just use Water. You look at it and Fire is weak against Rock. Not everyone knows that off the top of their head, yet there are some STRONG rock moves out there. I looked at a best counter list for Arcanine and not a single of the top 3 is a water type. I am right there with you man.
I prefer this one.
This one also lists the immunities, which now have different values on Pokemon Go.
Resist (1/2) is now 0.714x on PoGo.
Immunity (0) is now 0.5x on PoGo.
If you guys can get your hands on Pokemon Sun & Moon, it's the best game of the series to get to know immunities and resistances better. It has some new features to help players with that.