I've checked animal companion on the forum search and didn't find much. I heard that you get an armor check penalty to ride checks which is different than 3.5. I was trying to make a Gnome Pali with a riding dog, but that went out the window with the riding penalty with heavy armor. So, the next thing was a mount that I would not ride, but would fight beside me. I heard that there is a ruling that a Pali character can choose any Druid animial as his animal companion. Where is this ruling so I may have a print out for my character's records?
Yes, ACP is applied to the Ride skill. This does not mean, in my opinion, that heavy armor+mount=fail.
At low levels you won't probably be able to afford the heavy armor anyway and your mount is just an every day run of the mill horse or pony anyway. But keep your eyes on the goal, at 5th level there is a power boost.
Divine Bond is a 5th level ability. So, assuming you apply skill points to ride each level, at 5th level when you really start to use the ability, you have a +8 without Dex, +5 for level and +3 for class skill. Now by 5th level at the very worst you can afford MasterWork armor. Lets say MW Full Plate, with a hefty -5 ACP. Also So at 5th level without adding any Dex or any other bonuses you might be able to find you are a +3 on ride checks. Is that Awesome? No, but hardly an epic fail.
Bear in mind that you will most likely have a Combat Mount, so you will want to use the 2 tricks to train it Attack. That being said the ride skill DC needed to fight in combat then is 10, not a freebie, but it will be in several levels and it is a free action so even if it doesn't work it cost you nothing. That is just to get it to attack on top of your attack(s)
Guiding with knees and staying in the saddle are both DC 5 so a 2 or better at 5th level with a dex bonus of 0 and you still can fight even if your mount doesn't. Neither of these actions take one of your actions.
Fast mount or Dismount is still in doubt at 5th level yes, but every level that is just going to get easier and easier.
And to add another point, there are ways to make this even better. Money fixes some of it, Mithril drops that ACP way down. A couple of feats could also be helpful if you can spare them. Skill focus (ride) will eat up a lot of that, Animal Affinity also can pad that.
What I tell folks is if you want to be a mounted paladin you have to pay for it. You have to invest in it. You will be spending Skills, Feats and Money to make it work, but the pay off can be quite impressive.
From another source I found out that I can have any of the Druid's animal companions as long as it can be used as a mount. I like the big cat, I can't ride it till seventh level, but it is better than a camel or a horse. I don't see any other exotic mount that I could use that has four legs besides those mentioned. I havn't figured out what kind of mount I'll use till seventh level.
As for armor, I suppose I will have to use lighter armor than heavy armor. Such as breast plate and a buckler. I try to off set this with a dex of fourteen. Mithril stuff is way down the line.