Dragonrider
1)
The fantasy trope of riding a dragon mount in the form of a prestige class. It starts out in a familiar, scary vein: characters of all classes... but then makes it clear it is for meatheads... though the most common are barbarians, fighters, etc. Good save, fluff text! The chassis is d10 HD, full BAB, good FORT and WILL, with 2 skill points per level, and for some reason specific weapon proficiencies and ALL armor/shield proficiencies.
First level is dragonriding, which is a bonus to ride checks for riding dragons and somehow increasing the dragon's flight maneuverability by one level. Also, when on or adjacent to your dragon you are immune to frightful presence of dragons.
Second level is a boost to concentration checks for casting while riding, which you shouldn't really be doing because you shouldn't be a spellcaster. Ok, maybe a ranger or paladin. Fine.
Third level has a bonus feat from a small selection of mounted combat stuffs.
Fourth is being treated as having flyby attack, not actually granting flyby attack....Odd distinction and I don't think they would stack in any way if you also had the feat
Fifth is spur mount, which is a pretend ride check of DC 20 (you should have at least a +21 by now) to increase the dragon mount's speeds.
Fortunately this class is only five levels long! I think the mounted spellcasting is a bit off, but overall, all the abilities are good ones that make you better at riding dragons. I think REF would have made a bit more sense than WILL, but WILL is arguably better anyhow. I didn't think I would like this one at first, but it works. Look at what happens when WotC makes the PrC short and to the point! 12/14 I know I always have a comment about the artwork and I usually don't bring it up, but this one....Look at that shield. I understand it is supposed to look like an open dragon mouth, but it is a shield! Having a big HOLE in the middle defeats the purpose!!!

2)
This one seems a little trickier for me when it comes to opportunity costs. If you want to be a dragon rider, this gets you some handy stuff in rapid succession. Some can just be taken as feats, such as flyby attack and the bonus feat, but other things aren't so readily duplicated, such as the dragonriding and spur mount. I will hesitantly go with 3/4

3)
BAB is inevitable, the feats are useful for the class, the skill ranks are not bad, language is Simple, so minor it is! 2/2
Dragonrider 17/ 20