This is why I think the Aassimar will be so powerful, they only have to use 4 points to get the wisdom they need for the 4th circle, and then they can use only 4 points into charisma and still get a +2 bonus to all their charisma based skills and still have 22 points available for str/con/dex/int. The other races often have to spend 16 points to get to the same level.
Charisma is the paladin's best so it should be as high as possible. There are many reasons for that.
1) You receive Divine grace at 2nd level which adds the charisma modifier to all saving throws. So a 18 CHA paladin gets +4 to all saving throws. That is great indeed.
2) You receive Turn undead at 4th level and can use it (charisma modifier + 3) times per day. The strength of the turn undead use is also dependent upon the charisma modifier. This also applies to the number of undead affected by each turn undead.
3) You receive lay on hands at 2nd level and can heal charisma modifier * your level HP's per day. So a 9th level paladin with CHA 20 can heal 9 * 5 = 45 HP per day.
4) You have the paladin power Smite evil which adds the charisma modifier to the attack die roll and adds the paladin's level to the damage. So charisma is vital here too.
5) A paladin could choose the skill Diplomacy and this skill adds the charisma modifier to the skill rank.
6) Charisma also helps the feats Divine might, Divine shield and Divine resistance.
So a paladin should maximize his charisma attribute when creating his character. Only spending 4 build points and give CHA 12 (CHA 14 as an Aasimar) is not what I would recommend. What makes a paladin great is his charisma attribute as I showed above.
I would build my Aasimar paladin like this:
STR: 15 (8 bp)
DEX: 8 (0 bp)
INT: 12 (4 bp)
CON: 14 (6 bp)
WIS: 12 (4 bp) + 2 from Aasimar = 14
CHA: 16 (10 bp) + 2 from Aasimar = 18
If you choose Luck of heroes as your background trait you receive +1 AC and +1 to all saving throws to counter for receiving -1 AC and -1 to reflex saves for getting a poor DEX.
For skills I would choose: Concentration, Heal and Diplomacy. With INT 12 you receive +1 skill point per level. With the standard 2 sp per level for the paladin class you can use a total of 3 sp level which makes it possible to max out these 3 skills. Having INT 12 counters for the loss of 1 extra sp per level as humans get.
It's possible to have 10 dex and 10 int or 10 dex, 12 int, 12 con if you don't like an attribute below 10.
At level 4 you increase your strength attribute from 15 to 16 getting +3 to attack and damage. Pretty good for a paladin. All further attribute increases should to to charisma which gives you a charisma of 22 at level 20. That gives you a charisma modifier of +6.
For feats I would go for:
1th level: Power Attack
3rd level: Cleave
6th level: Divine might (or Divine shield)
9th level: Improved critical (longsword) unless you have a great longsword with the keen ability. Keen does NOT stack with improved critical in NWN2. It did stack in NWN1.
12th level: Divine shield (or Divine might)
15th level: Extra turning
18th level: Toughness (or Weapon focus (longsword) if you intend to become a Divine champion prestige class)
I think this could make a great paladin with few weaknesses. The key is to focus on charisma. With STR 16 (at level 4) you are strong enough to carry a lot of equipment, CON 14 is pretty good too. WIS 14 is just enough to cast all paladin spells. Remember also that magical items will probably increase the stats even further. In NWN1 I had a paladin in HoU with a modified CHA of more than 40. That is +15 to all saving throws, 600 hp per lay on hands, awesome smite evil, divine might and divine shield etc.