I'm not sure how representative this experience is, but I tried a trail of Wotr(beta maybe, cant remember), then got a mail 'in error' giving me the full game, then when Wotv came out, I was given it because i already had Wotr... I own both, but I did not pay any money for them (or want them, after 5 mins of playing wotr).
I bought M&B on recommendation of a rl friend (Byzantium_Supy0).
Pros:
Big battles
responsive control of chars in combat
Can pick up arrows etc fired by other ppl.
Brutal (an acquired taste surely)
Wide choice of gear.
Well implemented cavalry play (I hadnt seen that before in a game).
Cons:
Not incredibly pretty.
Does not alt+tab very happily.
I bought Chivalry because colleagues wanted to play some medieval lan battles at lunchtimes. They thought M&B didnt look (aesthetically) very good, so we (~15ppl) got chivalry.
Pros:
Taunt animations.
Dismemberment.
Quite pretty.
Cons
Small battles,
Limited gear,
Combat feels unresponsive often
No fine control of weapon (left click is always swing, timing determines direction).