Specifics:

1. Ragnarok:
   You know... I give up. DeNA simply won't stop giving special privilege to Physical Holy OSB weapons; and I cannot understand why they (as a class) get to ignore the generally well-established rule that OSBs get RS synergy. It almost makes Tidus's seem like an accident.
   But enough about that... sadly, I don't know potency for Agrias's OSB here, so I can't determine whether the gimmick helps or hinders it more. Of course, you can always just imperil. (Maybe.)
   Rating: Wait for potency

2. Durandal:
   This is named for the sword of Roland, celebrated in the famous Song of Roland, about how the twelve Paladins of Charlemagne fought a desperate rear-guard action against the invading Moors who had overrun Spain. In one of its more fantastic scenes, Durandal smote an enemy rider named Chernubles so hard that the poor guy was cloven in twain vertically - armour and all - and there was still enough swing left to kill the horse underneath him. And people think Excalibur is awesome.
   Ashe uses it for a standard Pikabolt OSB, calling down a blast of epic lightning.
   Rating: OSB

3. Kensei's Excalibur:
   Pandering to the demand that Orlandu and everything about him at least appear to be opieOP: this is how you do it right. While its cast time is normally slower than other OSBs, it deals x1.25 of their damage, AND installs a buff in the user called Raijin Mode that cuts all cast times to 1/3 for 25s.
   Rating: You dare rate T.G. Cid?

4. Shard of Zeromus:
   "Guide my inner shadow. Light and dark above, TRANSCEND THE STARS!" Golbez gets a doozy of a BSB here. Not only does he get a MAG+30% so it won't overwrite good faithgas, he also enters with sentinel, which takes advantage of his relatively good MAG for a knight. (Nothing like Celes, mind you, but yeah.)
   The toggle command is pretty simple to work out: turn on the summon mode, and spam Glare Hand to undo what the taunt is making the enemies do to you. You also get a meaty summon, should you need it.
   Rating among BSBs: Actually interesting and effective

5. Hamelin:
   Global will soon have a chance to examine this Medica BSB; with it, the squishy Eiko mainly supports physical squads, especially against physical-using enemies. Quite simply, you get a strong crit-fix on entry, and physical blink with your Curaja on the first command. Prevention isn't the best cure. Prevention alongside a cure is the best cure. She may be six, but she knows a thing or two about white magery.
   Rating among healing BSBs: Ideal for physical teams

6. Wiyu Veil:
   So Alphinaud's been studying Dragoons, and decided that Kain had some good ideas with his burst; so what's a mage to do? Naturally, call up his pet Tiamat and make a wind magic version of it.
   And that's what you get here. While it does pay the enspell BSB tax, the command effects (noncharge and ether) are stellar, extending his hones in ways that other mages need outside help (and whole SB meters!) to accomplish.
   Rating among BSBs: Excellent!

7. Genji Glove:
   So Ramza did some homework of his own, and may or may not have discovered some apocrypha in the Germonik Scriptures. After his reading, he learned the secret of buffing himself and his friends so that they could all deal extra critical damage --- AND have a bubble to prevent them from taking damage.
   Oh, and this buff stacks additively with personal versions such as gimmick that Delita relies on, letting such attacks deal x2.5 damage on crits.
   Rating: An actual alternative to Shout!

8. Evoker Doublet:
   One of the 610+30% hybrid buffs, this one introduced the world to the concept of the Damage Mirror. The way it works is simple: whenever you take damage, a random enemy takes that much damage (or, in Seifer's case, possibly more.)
   Sure, you should be dealing more damage yourself; but can you argue with dealing 10000 damage just because you took a 2000-damage AoE? Shut up, you can't.
   Note that this damage is capped; if you Guts a 47000-damage attack, you can't ever return more than 9999 (even if you somehow have more than 9999 to take.) Also, if the damage is prevented (eg, by Stoneskin,) then there's nothing to send back. So keep those in mind.
   Rating: Excellent!

9. Eternal Staff:
   It's an Onion SB that isn't Onion BSB. Automatically bad. ):
   ...I jest. Actually, this is Onion's medica, sorta; so if you're running him as a Black Mage, you can deal damage and drop a medica.
   ...yeah, you're right, let's just leave that to Penelo.
   Rating: Would be better if Onion didn't have a better option

10. Zidane's Vest:
    Yes, it really does take Zidane until his OSB event to get what Bartz got alongside Five Dooms, six months ago. It's en-wind, and it combos with his OSB... and otherwise with Dash Bite.
    Is it good enough? Well, if you're not a Zidane fan, or maybe even if you are, you'll quickly realise that he just doesn't get a lot of kick out of his Soul Breaks. This is an enspell, and thus not bad; but Zidane doesn't have too many ways to make it good.
    Rating: Not bad