Both shields are great items, each fight is going to have different out comes for what you choose to use, and luckily before you engage you are given the option as to which you want to use, or if you don't care about using WSs then shield swap.
I know in a number of Voidwatch fights there are times where Aegis will easily be more beneficial then Ochain, and other fights where Ochain will pull ahead, neither of the shields are better or worse then the two so I don't see why there is even a debate they're both good, anyone who has otherwise to say is just blind and can't get past it cause they own one but not the other, and so they pick their favorite because they got to play with it for so long and they don't want to think that their favorite toy is replaced or has an equal.
Everytime I read lolAegis or lolOchain I can click the person making a response and see that they don't have one or the other.
I also sure as hell know Aegis or Ochain doesn't make or break the Paladin that's for sure, it just requires less to actually play the job, I've seen plenty of fail Ochain and Aegis players to know this.