All of the available cross class skills are pretty situational and quite minor, in all honesty. But there's certainly some ones that are worth it.

Foresight is obvious, though it's only a 5% damage reduction I believe on average. Pop it constantly on trash pulls rather than rely on it as a heavy cooldown for big hits.

Bloodbath isnt anywhere near as effective for a Paladin as it is for a Warrior, but it's still nice sustain. It wont save your life ever so don't save it. Instead, keep it on cooldown and pop it every time you pop Fight or Flight. They both have 90 second cooldown and FoF will make BB 30% more effective. I have FoF + BB macroed onto the front of my Fast Blade to ensure they're always on cooldown.

Cure and Stoneskin are both worth taking, however they're situational. Cure doesnt output enough healing to heal through anything big hitting you but can be used to top yourself up in periods of less boss damage, like when the boss leaps away to do a special move (eg, Ifrits dashes etc). Stoneskin is the same - you wont use it that much, but it's really handy on SOME encounters where you get a period of quiet to cast it. The best example of a good use of Stoneskin is Ifrit Hard - when he lands in the middle and everyone takes a big aoe hit, cast stoneskin afterwards before he returns to hit you again, as healers will still be AOE healing the raid.

Those four are all vital imo. As for the fifth... well. Protect is nice when solo but useless in a group. Raise is nice to have on your bars for efficiency but wont make a difference in combat. Fracture is a tiny tiny DPS boost if used but actually a threat -loss- so it's rarely worth using. Mercy Stroke isnt bad but a single off GCD hit every 90 seconds is negligible. All of those are a very minor difference.