Smite is your main DPS skill, but when you go STR/SPR you are more focused on support than the INT/SPR variation (funny, I know). Smite and Conviction are there to add some damage, but most of the time you will be doing a little DPS with Sacrament + Blessing autos. This combo makes it so everytime you auto Blessing procs off twice.
Not only do you have the 10% base heal from Cleric’s Heal without investing any points, but you have a really good Mass Heal due to SPR. This makes it so you have good buffs, a good amount of heals, and some DPS just so you don’t sit around and do nothing when buffs/heals aren’t needed.
Those two fill slightly different roles. Where the Paladin shines is dealing with elemental/magic damage, be it by decreasing the damage your allies take from it, or by increasing that which they deal. The Priest/Krivis choice just changes slightly the role you will fill as a Paladin. Krivis is a semi-support caster, while Priest is a full support class.
The Krivis (or INT) variation is a pseudo-support with more DPS. You have burst heal with Cleric’s heal, you have DPS with Zaibas, as well as a couple debuffs/buffs. The main thing you bring is damage, Krivis’ crit from Zalciai, and extra buff slots from Daino. This is very good when you are running with another support class in the group, like a Priest, who has lots of buffs.
The Priest (or STR, which I almost want to call SPR) variation is a more support oriented variation. As mentioned above, you have 10% HP healing on Cleric’s Heal, and the SPR will add to your Mass Heal. You also have very strong buffs on Aspersion, and the Bless+Sacrament combo, not to mention freaking Resist Elements (I have a thing for this skill). Deprotect Zone and Monsterance are nice to reduce monster defenses, and both scale up with your SPR. The main reason you get some STR and go for Smite here is because the only form of DPS you have is 1) using Aspersion offensively, or 2) using those tasty Blessed attacks.