What level are you starting at? A lot of the discussion in this thread has revolved around the possible roles of a tank. Many, including myself, are proponents of the tank as damage shield/sponge. However, this is only really valuable if there are other party members that can lay out the damage. If you are starting at 5th level and your casters can drop fireballs, then you can start as the high ac, low damage, I'm just keeping you busy while you're nuked down kind of fighter/paladin. However, if you are starting at level one as the only melee character, know that the rest of the party is going to have a hard time putting down the enemies. They will have very limited spell slots for attack/healing magic, and negligible melee. Melees generally carry the casters to 5th level and then the roles reverse and the melees support the casters.
If you really want to play a paladin over a fighter, then weapon focus is almost required at first level. Without the high strength, your hit mod will suck. For instance, your 15str Aasimar will have a hit mod of +3 (+2 to damage/+3 with two hands), compared to a level 2 fighter with 18 str at level 2 with power attack, cleave, and weapon focus and a +7 to hit (and +4 to damage/+6 with two hands). One of the biggest strengths of the 16 or 18str level one fighter is power attack/cleave. When you can start with a +4 or +5 hit mod and lay out the monsters you fight, usually in one hit, and generate extra attacks, you can save your party a lot of damage. You can still do this with a reasonable AC, and you can still switch to a higher AC, lower damage style later in your career.
Also, in a feat poor Paladin build, leave the bastard sword alone. You can get all the same benefits from a long sword save the d10 vs the d8. The feat is not worth the single point of average damage unless you just have a high character concept/roleplay desire to wield a bastard sword.
It sounds like you have a strong roleplaying preference for the holy warrior type. The aasimar are a great rp hook, and the paladin is not a bad class by any stretch, but as the party's tank, I'd think twice about the ECL race. You'll need all the hp you can get. I don't have any books in front of me, but what are Torm's domains? I encourage you to have a look at the human Clr1/FtrX build. If you worship Kord, the strength and luck domains are a great bargain. When you've accumulated the feats you want/need, you can always dip back into cleric for a bit more casting utility with no multiclass penalty, or stick with fighter levels to be less buff reliant. Alternatively, you can simply switch the build and be Ftr1/ClrX and still be a great "holy warrior" if a bit more dependent on buffs, although, you'll also have a great deal of self healing and utility spells.
Ok, this is getting long. The last thing I want to do is to give a paladin alternative.
Human Pal6 Ftr4
Stats (using what you rolled)
Str: 17
Dex: 14
Con: 16
Int: 10
Wis: 13
Cha: 15
Progression:
Ftr 1: Power Attack, Cleave, Weapon Focus (Greatsword)
Ftr 1/Pal 1:
Ftr 1/Pal 2: Improved Buckler Defense
Ftr 2/Pal 2: Dodge (put stat up into charisma)
Ftr 2/Pal 3:
Ftr 2/Pal 4: Divine Might
Ftr 3/Pal 4:
Ftr 4/Pal 4: Mobility (put stat up into strength)
Ftr 5/Pal 4: Spring Attack
Ftr 6/Pal 4: Weapon Specialization (Greatsword)
Alternatively,
Swap Dex and Cha
Progression:
Ftr 1: Power Attack, Cleave, Weapon Focus (Longsword)
Ftr 1/Pal 1:
Ftr 1/Pal 2: Two Weapon Fighting
Ftr 2/Pal 2: Improved Shield Bash (put stat up into strength)
Ftr 2/Pal 3:
Ftr 2/Pal 4: Divine Might
Ftr 3/Pal 4:
Ftr 4/Pal 4: Dodge (put stat up into strength)
Ftr 5/Pal 4: Mobility
Ftr 6/Pal 4: Spring Attack
Get a spiked light shield, with the defending property on the shield spikes. You can make a single attack with it without losing the AC bonus and you can allocate the spikes enhancement bonus to your AC.
I prefer the first build, since it uses your diety's favored weapon, but the second will give you a higher AC at the cost of a bit of damage, and 1 to all your saves.
Good luck in your campaign.
