How much skill you "need" depends on your build and what you want the shield for.
If you're a hoplite/thrower, I'd recommend a board, kite, or norman shield. Get at least 3 shield skill. The wide area of the shields will make up for your lower skill (higher shield skill increases your block radius beyond the stats and physical model of the shield). They will catch as many arrows as you will need in a battle/siege round, but will break against strength-based melee attackers.
If you can spare 4-5 shield skill (it's really not that much of an investment), the knightly heater, heavy round, and plate covered round shield are all great choices. The knightly heater shield has fast blocking, which is good when you are using spear+shield against other melee. The heavy round shield and plate covered round shield will last a long time against anything that isn't an axe.
I haven't used the hand pavise, but it is similar to the knightly heater shield. Good durability with quick blocking speed.
Don't forget to pick a shield that looks good with the rest of your equipment! There's many options, and unless you are 100% set on getting THE BEST GEAR for your build (skill counts more than gear anyway), make your items aesthetically pleasing to yourself.