First, the preserved stuff: St. Louis and
Close-up of neck:
I love the shape you get from the St. Louis pattern, which can be found in Dorothy Burnham's 1970s book Cut my cote (which I have in Swedish: Skjortor, särkar och blusar : traditionella mönster från hela världen : historik och tillskärning), or from Marc Carlson's webpage "Some Clothing of the Middle Ages, here.
Since most garments of this period are unisex I made my most recent shift from the St. Louis pattern.
And reincorced the neck with this lovely vintage twill linen ribbon
Next time I will make the loser sleeves narrower to fit better under tight undersleeves, but it works just folding them too.
Louis had a sister, who also had underwear apparently: The shift of Isabella de France, from Kostym.cz
Here's a Spanish female shift, which once belonged to Dona Teresa Gil, who died in 1307.
Photo from the Nonullusblog on history.
I haven't seen any pattern drawings from this one yet, but that may be because my Spanish is non-existent.
That was the preserved examples. When it comes to depictions of underwear I can't post all of course, hence the word "favourite" in the post's title.
Women in underwear are even more rare than naked women, but here's one from the Maciejowski Bible, in bed after giving birth.
Photo from Medieval Tymes
This a recent favourite: Lancelot, escaping in his underwear after being tricked into sleeping with Sir Pelles daughter Elaine (that's how Galahad was made). Add. Ms 5474 fol 150v, last quarter of the 13th century.
Photo from British Library' Medieval manuscripts blog
And then there's the lovely shirt from Cantigas de Santa Maria:
And a pair of braies from England, from the Trinity Apocalypse, MS R. 16.2, Trinity College, Cambridge: