My deciding factor is type of hook and line size. If I am using light line and/or light wire hook (finesse jig), I go with a medium to medium heavy. If I am using heavy line and/or a heavy wire hook, I go with a medium heavy to heavy action rod.
The lighter action rod will keep you from straightening your hooks out and breaking line on hook sets, the heavy action rod is built with power to penetrate a heavy wire hook into flesh.
Think of a needle (light wire hook), does not take mush pressure to put into skin. Then think of a phillips head screw driver, it will need a little more force to penetrate.
I urge you to call Dave Settle at www.customanglerods.com. If there were doctors of rod building, Dave is this man. He loves to talk rods and will answer your questions better than many.

How close should you flip a jig into thick cover? That is the question!

Be sure to get you a set up that's gonna be balanced weight wise. Flipping, Carolina, Jigging can be exhausting if you have a rod that's gonna work you to death

Medium heavy is correct. A MH rod is better than a medium for hook penetration,and you can also Pitch a MH better than a heavy action rod. 6:3 to 1 reel ratio is preferred by the Illustrious FZ1.

I've had times when it seems that they won't hit the bludgeon type baits that are used a lot in flipping. When that happens it seems that I can get more bites by going to smaller lighter lures on 15# test and a medium heavy casting (not flipping) rod. You risk losing a big fish but can make up for it with numbers of smaller ones.

I fish mini jigs 1/4 oz plus trailer and use a MH 8' saltwater castaway casting rod that bass can bend almost double and have landed bass in the 9# class.Fish mostly Eagle Mt and other local lakes that don`t have heavy cover.The most work they do is getting them out from under docks .With the light wire hook on mini jigs you don`t need a rod that will drive a nail into wood.But what you do need is a rod with some give so they don`t tear the the hook out or strighten them.Landed a cat over 20# on this rod with no problem.

I know we all have opinions and beliefs and they can be very different at times.. But my reason for working a Jig or even a plastic like a brush hog on a heavy action rod is because I believe the fish bites on the head of the jig or weight and holds that part of the bait tightly and if you don't have a heavy action rod with low stretch line you will not be able to get the head of the bait away from the fish and the hook set. Even a good set on heavy mono with a MH rod still will most likely not budge the head of the bait meaning halfway through the fight the fish gives up on that bit of food and lets go.... Like I said just my opinion.

Jody