Huh PD has nothing to do with xbows... the only requirement is strenght and on horse u can only use light xbow which has a req of 7 str.
In resumé (tried both ones HX and HA):
HA:
pros:
-higher fire rate = more damage over time
cons:
-Needs more str = less agi = less HA skill = bigger penalty to accuracy AND damage while riding a horse + cut (damage type) so heavy armored guys will laugh at u.
-less agi (need more str) so less riding so slower and less maneuver on horse.
-takes a really long time before you do decent (lots of lvls and grinding while feeling nearly useless) but if ur good enough, it can be really worth it.
HX:
pros:
- slower firing rate but a lot higher damage per shot (pierce type of damage + higher HA skill)
- is fun to play really early (around lvl 15 you can do decent cuz as soon as u have 7 str, u can start pumping agi)
- you can get super freaking fast and maneuver on horse (can easily reach 10 riding!)
- with more agi you can get more HA skill (5 HA) so almost no penalty to damage and accuracy
- low upkeep even with a good horse like the courser
Cons:
-fragile (no ironflesh and only 7 str means not much is needed, while running full speed on horse, to kill you.)
- slower reloading speed than on foot so u need to put all ur wpf in xbow to get a decent reloading speed.
- slow firing speed (of course)
- with that low str, u cant use any good weapon or armor.
- once ur dehorsed ur more than screwed (cant do anything beside running pretty much)
I need to say though that i really like both but my favorite for a funny yet quite effective horse build is the HX, if used correctly, it can be really effective. A couple of times in a single day of playing session i managed to get good k/d ratios a lot of times with it and even annoy some good cavs and infantry 2-handers ;)
If u have any other questions regarding HA or HX or about xbows, feel free to PM me