When it comes to how individual men at arms decided on one piece of armour or another, it's hard to say why they made their decisions. Though we have a trove of documentary evidence from the 15th century, including many entries in inventories, ordinances for soldiers' equipment and even at least one letter from an armourer to a client, I have never seen anything as clear cut as 'I would lyke to were thys helmyt, because it gyves better vision, and the chance of being stabbed in the face is worthe that swete aire flowe'*. The 'why' of armour in general is often elusive, even though it is often the first thing that generations of scholars have jumped on when explaining changing forms. Since the wearers are dead, and since they wrote little of the 'why' themselves, we are left with inferences, many of them tenuous.

Still, we can -infer- the existence of personal preference, and we can discuss the interplay of style and practical needs. The first question is - were their helmet-choices- at all in the 15th century? The answer is generally yes, but that it was constrained by convention, fashion and technology. Looking at documentary evidence and pictorial records, given regions in different periods often strongly prefer one type of helmet or the other, but it is rarely fully uniform. For instance, in the beginning of the century, the visored bascinet with a mail aventail was worn in much of Europe, but in some places, like Germany or France, fully armoured men at arms might wear a kettle hat. Then in the 1410's the great bascinet was popularized in northwestern Europe and various forms of armet in Italy, and then in the 1430's the sallet begins to become popular in France and becomes the most common type of helmet outside of Italy by around 1460 or so. But within these general trends, we see individual variation, which points to individual preference. In the 1410's and 1420's in England we see a combination of the older bascinets with the new 'great' bascinets, while in France in the 1430's we see both great bascinets and sallets. In Iberia kettle hats are common in the form of the 'cabasset' but sallets are also worn. Inventories often describe multiple helmet types concurrently, and art often shows multiple helmets in use side-by-side, like the Beauchamp Pageant from England in the 1480's. Toward the end of the century we see a variety of new helmets introduced which deal with some of the weaknesses of the then-dominant sallet. So there definitely were different types of helmet to choose from at a given time and in a given place, though there were also helmets that were more or less typical of a time and place.

Many of these instances of diversity are in times of stylstic transition, and so some of the variety may come from older helmets being worn - possibly by older soldiers who preferred the equipment they were used to, or by those who wished to spare the expense of buying a new helmet. However some of it may well have been personal, practical preference. A bascinet with an anventail provides excellent mobility to the head, but it is relatively heavy (much of the weight is born by your head, and the aventail weighs quite a lot) and the mail around the throat is a significant vulnerability. The great bascinet takes the weight off of the neck entirely, because the helmet rests on the shoulders, and it protects the throat with metal plates. However, you can't turn your head in a great bascinet except inside the helmet itself - at least one of the neck plates is strapped to your cuirass. A sallet and bevor offers a good balance of protection and mobility, but the two piece construction means that gaps can open between the bevor and visor, allowing a lance or some other weapon to slip between them and into the wearer's face. Armets offer decent protection and decent mobility, but in their 'heavy' form, with a wrapper strapped to the front and gorget plates extented below, they lose much of that mobility.

We can see that people were aware of the strengths and weaknesses of armour by looking at how they improved it over the years. In the 1470's and 1480's, armourers began making sallets where the bevor and visor pivoted from one point. The pivot means that the visor and bevor can no longer gap in the same way, since the bevor is now integrated into the helmet. Interestingly, some of these helmets appear to be 'retrofitted' sallet, which shows how motivated wearers could be to adapt their equipment (or how eager sellers were to 'spruce up' older armour in the resale market). In time, this form became the close helm of the 16th century.

Regarding gauntlets, 'finger' gauntlets are the original style of gauntlets in the early 15th century, carrying over from the 14th. It is only as the 15th century wears on that mitten gauntlets develop and gain popularity - first in Italy, probably, then spreading to the rest of Europe. The advantages of mitten gauntlets is simple - they protect the hand and fingers much better, since they protect the fingers from being smashed as well as from being shopped or sliced. While they restrict the motion of the fingers, very few actions on a medieval battlefield strictly need the fingers - wearing mitten gauntlets men at arms could hold reigns and wield a sword, pollaxe or lance. In some forms in 15th century Italy they become single-piece rigid protectors for the entire left hand (while the right gauntlet retains articulation so that the wearer can wield a sword.) On the other hand, there are also a lot of combination 'mitten/finger gauntlets that you see in Italy, England, Spain and elsewhere, where much of the fingers are protected by extended plates from the hand but each finger still has independent defenses. Here is an English example. These appear to be an attempt to combine protection and dexterity. But still, since finger dexterity isn't essential to fight in a medieval battle, mitten gauntlets don't appear to have been more than an annoyance.

Sourches:

Tobias Capwell - Armour of the English Knight 1400-1450

Claud Blair - European Armour 1066-1700

Tobias Capwell - A helmet in the Church of Bury St Edmonds

*Not that anyone would actually have written it like that. Their middle English spelling and usage would have been better.