For levelling and tanking pre-70, SoC and SoR are both better, because most of your gear will have spelldmg on it if you are following Blizzard's planned loot curve for Paladins.
However...
I recently tried a Retadin on the PTR with a stack of PvP and SSC/TK gear (all Arms-Warrior stuff) and dear GOD does Seal of Blood rock then... it is absolutely amazing for PvE DPS, it outdamages Seal of Command considerably and is much less burst-oriented, making your threat easier to manage. Additionally, the 10% recoil is actually helpful, because your healers then give you a weak HoT to take care of it which recharges your mana and keeps you swinging.
For the level you get it I can see no use for SoB, but seriously, once you get that Merciless two-hander and a lot of purple pixels the strength of it really shines through... While it is true that Seal of Vengeance is better for tanking and scales with spelldmg, if you compare itemisation points SoB gives you a lot more for your money, and unlike SoV and SoR it benefits from your crit stat as of course, neither of those are capable of a critical strike.
To give you a rough idea about PvP utility, I brought down an equal-geared Arms Warrior with it; simply killed him before he killed me.
~sins