Which one do paladins usually take for their last talent? Seraphim still?
All three are strong options.
Last Defender is typically only used in M+; it’s always good value on trash, and is best on fortified weeks or weeks where you can do big multipulls.
Righteous Protector is a great defensive option for raid bosses. Very rare to see this used in M+, but there is a meme build based around high wings uptime.
Seraphim is a good all-round option; good DPS (though LD can be higher on AOE), good all-round defensive value, and a great choice against high magic damage.
Normally i do like, when tyrannical week i go seraphim, when fortified i go last defender. Righteous Protector is for Raid.
Also note that last defender is really strong in horrific visions, too. The amount of mobs you can pull at one time increasing your damage to the point of a ret paladin is ridiculous; especially when you can click your cloak to negate much of the sanity drain during a huge pull.
Sera generally, LD for hard m+ keys, RP if you’re an alt that doesn’t want to/have time to learn the class and just don’t wanna die in raid.