first of, the idea is at least most of the time be with a mount \ companion.
mounted isnt the right word, it's more fight with a animal at your side \ mounted.
my race will be human or 1/2 orc as i like to do damage and maneuvers.
i will use in all options below, the undersized mount so the mount will be medium OR partly medium (reduce animal always on).
top allowed is one level dip.
classes allowed are the list below only.
1) Cavalier order of the dragon, beast rider Emissary and honor guard.
mount will be : a gecko or a bear .
you take all the mounted feats but also the swift aid feat.
the idea is to charge if \ when you can for a lot less damage than order of the sword on a big mount, but still decent. than full attack while you bodyguard your allies and mount.
it's not a super DPR build, but a decent one that also assist well it's friends .
dip here isnt needed.
2) same as 1, but order of the sword and no honor gaurd.
mount need to be a mobile 1 - like the gecko.
the idea is to move in-out-in again.
it's DPR is very nice - but.... i think some what boring and a 1 trick pony.
3) Ranger, beastmaster. combat style = mounted.
mount = a flyer that stay medium - a giant vulture or a roc are the best.
when possible you make mounted charges, when not you are a full ranger with a VERY nice companion.
use Reduce Animal all the time - so mount stay medium at all levels - it's damage will be nice .
use carry companion to make mount begone when not needed - and you are still a decent full stealth ranger with power attack and some spells.
4) hunter, AC will be a deadly one - large cat, Trex, roc etc.
or even a ape - that dm allow (if int is 3+) to wield a weapon.
with team feats - your total to hit is almost like a full bab.
the mount will be deadly. use Reduce Animal at all times.
use reach weapon and precise strike.
i didint do the math, but the extra 1d6 per attack and the + to str will make you and your AC decent + in damage with great reach.
another one to consider: sohei monk.
take the nature soul and animal ally feats for an appropriate mount (hint: one with pounce), then boon companion to match it's advancement to yours.
a reason for this:
sohei monks get loads of bonuses for their mounts, can flurry with polearms and spears, can flurry while wearing armor, and can take any mounted feat at any level they want via bonus feats.
mounted skirmisher at level 1-2? you betcha.
way too feat intensive
a sohei mounted is amazing but ALL your feats will go there.
(as i want mount to NOT be large) it's
ride by attack
3 feats to gain a mount.
human, level 11, monk has 11 feats. leaving 2 feats on NON mounted.
so, i prefer the above options really.