The battle bard is probably the most epic and awesome of all playstyles in ffxi. Nothing says hardcore like a crazy lute solo followed by smashing an NM with your dinky little daggers.
But in all seriousness SE has recently been handing bard quite a large selection of powerful damage dealing gear, and as of the last update bard relic+2 body is actually something else.
Note: Military parade here gives +10 str/dex/agi while engaged. Or more? I heard reports its 16 for +2
So, first and most important question, why battle bard? Well most importantly, a bard subbing ninja allows you to cover 2 entire sets of yellow procs in abyssea. This is pretty important as it lowers the amount of jobs and people you need to do the fight. A brd/nin + blm + whm/rdm cover all but blue mage procs in abyssea.
So, lets start with daggers:
Bard has access to only a handful of the daggers dancer and thief have, however the few they do have are also some of the best daggers in the game. Bard can even use Mandau, a dagger dancer doesn't even have access too!
Probably the most important dagger to look at is this bad boy:
This is probably the only option for offhand for bard. As nice as it is to maximize DPS, the other bonuses provided by this dagger kind of take a priority. But it's ok! This is one of the top offhand daggers for brd even DPS wise. There are slightly better and if you personally want to go for a higher DPS build that's fine, however you can't go wrong with this.
As for mainhands, we have a few options.
Probably the best mainhand for bard. Rudra's storm is a powerful weaponskill and pushes bard right up to the front line.
The second best dagger for bard, Mandau provides an incredible amount of damage. This might even situationally be the best dagger for bard due to our access to some of the best str/dex gear in ffxi, like hecatomb's.
The third and fourth best daggers for bard, however good luck getting either of these from voidwatch. If you can get your hands on them, congratulations!
Now, as for daggers that are actually possible to get for the average player, we have 2 prime contenders for mainhands:
Both of these daggers provide different bonuses, however as far as I know the double attack dagger comes out on top for overall DPS. Not 100% sure. Either way the difference between them dps wise is marginal, so if one is better than the other, its by only a small amount. Can't go wrong with either of these.
Moving on to sub jobs! Primarily we have only 2 choices. /dnc, and /nin. If we're talking about yellow proccing in abyssea, /nin is really the only way to go, though /dnc is pretty good if someone else can sub ninja, and /dnc lets you keep yourself alive much easier.
And now for some gear sets! First off, Externator is hands down the best weaponskill for bard, bar Mercy Stroke and Rudra's, so let's look at what we have for each of these three weaponskills:
Externator
Rudra's
Mercy Stroke
And finally, here' a pretty solid example of a TPing build:
http://www.ffxiah.com/item-sets/213276
Some important pieces to note for bard, particularly our instruments, since switching instruments doesn't reset TP for whatever reason, (I'm not complaining)
An important instrument for hitting the haste cap on bard.
And:
For the most part, our best instrument for weaponskilling. +4 attack is nice to swap in, though I think if we swap to an ammo item and then back to an instrument it doesn't turn off TP. Not 100% sure about that one, but there might be some ammo slot items worth looking at if you can swap to them.
I do know going from empty slots -> instrument doesn't affect TP, so going ammo -> instrument shouldn't either, however going instrument -> ammo may. Needs testing.