The point about PrCs being a trap is pretty valid. You really need to advance 2 or 3 of Mount, LoH, Spellcasting, and Smite Evil in order for it to be really good, otherwise you just need some really good features to come out of it (like using Pious Templar as an "accelerated" spell progression class for paladins, and using it's free Weapon Specialization to get MWM and something like Driving Assault or Slashing Flurry).
Lots of Paladin variants give up the mount, however, and make other PrCs less of a trap. For example, the Healing Spirit ACF makes Gray Guard a much better PrC, since the only thing Gray Guard absolutely doesn't advance is the Mount (and it's un-restricting of Smite Evil is ridiculously useful).
Ok, this thread has actually re-invoked my interest in versatile Paladins.
Duskling Fighter 1/Paladin 4/Gray Guard 2/Divine Champion 1/Gray Guard 2/Contemplative 1/Ordained Champion 3/Gray Guard +6
1) Point Blank Shot, Precise Shot, Rapid Shot, Charming The Arrow
3) Weapon Focus [longbow]
6) Extra Smite
9) Ranged Smite Evil
12) Rapid Shot, Manyshot (from Ordained Champion), Nimbus of Light (from re-training), Stigmata (from level)
15) Practiced Spellcaster [Divine Champion]
18) Extra Smite
Domains: War mandatory, Protection highly recommended, Incarnum and Time are of notable use. 3 total.
Starting stats: 18 Cha, 13 Dex, 14 Con (+2), 12 Int (-2), 12 Wis, remainder doesn't matter.
Smite Evil: ~+12 to hit, +18 damage (+72 damage on a Manyshot), 7/day
LoH: 14th level Paladin, ~168 hp LoH healing pool (better known as 33 ability score points with Caduceus of Healing)
Oh, and you have the whole "punch people so hard they lose all their magic" thing going for you, too.
As an analogue to this build, there's a melee version, too:
Human w/ Paladin 5/Fighter 0/Rest same
1) Weapon Focus [some melee], Power Attack, Improved Bull Rush, Battle Jump
3) Cleave
6) Leap Attack
9) Combat Brute
12) Improved Overrun, Shock Trooper (from Ordained Champion), Nimbus of Light (from re-training Cleave), Stigmata (from level)
15) Practiced Spellcaster [Divine Champion]
18) Extra Smite
Domains: Wrath, Protection, War