Hey Drachillix - what kingdom? Meridies here…
I have fought with many different shield styles: scutums, kites, strapped rounds, centergrip rounds, centergrip ovals, bucklers, pavises, and heaters.
The scutum (a large rectangular shield, popularized by the Romans) was an excellent war shield, in that it provided enormous protection. It was also VERY heavy, and without having the time to dedicate to daily training using it, very tiring to use. It also has the effect of defending your enemy nearly as much as it defends you - it’s hard to maneuver a weapon around it. When used in formation with other scutums, it makes a very tough defensive barrier, but the wielder is pretty much just a living wall of blocking - its up to the spears behind you to take out the people in front of you.
Kites are a far more favorable style, to me, for a war shield. They are much easier to carry, and though they offer less total coverare, they can easily protect the majority of your body without trading off mobility/carrying weight. They don’t interlock as well as the scutums do, so a shield wall of kites is not going to hold a charge the way a shield wall will, but at least you can swing a weapon around one with relative ease.
Strapped rounds are very much like kites without leg protection. I actually think you can create a stronger shield wall with strapped rounds than kites, because you can have the front line kneel and a second line overlap their shields over the front line - the point of the kite makes this hard to do. In single combat, a strapped round is at a heavy disadvantage due to the distance it needs to move to protect the legs.
A centergrip round/oval makes this movement easier - in fact, centergrips in general are a lot quicker to move because you can pivot them around a single point, instead of around two on a strapped shield. However, as excellent as they are at single defense, they are a lot more vulnerable in mass combar because they can be pivoted so easily. In single combat, a centergrip fighter can move their feet to flow with the pivot, but in mass, its not always possible.
Bucklers are like tiny centergrip rounds - very fast, very effective if you actively punch block your opponents blade, but you have got to be quick and observant to not be torn apart when using one. Interestingly enough, they make excellent shields against polearms and spear weapons, as they focus more on redirection than blocking…and if you can get close, they are maneuverable enough to block buttspikes and backup weapons.
Pavises range from a form of centergrip heater-like shield to thinner scutum style shields. Lighter, maneuverable, but still vulnerable to pivoting and harder to carry long term than a strapped shield.
Heaters are my first choice in shields, and what I fight with these days. The have most of the protection of a kite, but with out a portion of the top and not as long, so they are a good bit lighter. Strapped properly, the corners of a heater provide excellent visibility while still imposing enough of a defense to keep that visibility from becoming a vulnerability. Often, a very slight movement of one’s body will shift the corner enough to completely rob the power from an incoming blow.
Hibernicus - personally, no. I am pretty good - I’ve been studying medieval tactics and warfare for 10+ years…but it is nothing compared to the daily practice and life of an ancient man at arms. Just as none of them could come and do my daily job, there is no way I could go back and do theirs as effectively. That’s not to say I couldn’t learn to, but I don’t think my own understanding of tactics and such would outweigh theirs.
Unless, of course, it was for a specific battle where conditions outside of skill at arms were a factor. I could, for instance, tell the french that charging into a mired, swampy, muddy bottleneck at Agincourt would be a terrible idea…
…but why would I? I always fight for the English. For God, Saint George, and King Henry!