I have seen there were various forms of certain items of armour throughout 15th century and I am curious how did they come about, and in generally how were they different from one another?

For example there were several different types of helmets like sallets, kettle hats, bascinets, capacetes, morions... Did some have advantages or disadvantages against certain weapons or other functional differences, or was the difference only in style? How would a soldier choose which one to use? if he even had a choice that is?

Also I noticed that plate gauntlets were most commonly only "mitten" style gauntlets. When did the normal "finger" style gauntlet develop? How flexible/usable were these plate mitten gauntlets anyway?