Based on my experiences I have written some brief thoughts I have about Bretonnian Paladin Battle standard Bearers (BSB)...

Every Bretonnian general is very familiar with the BSB - it is an obligatory character and a free upgrade to our hero. So every Bretonnian army will have one. I also believe that almost everyone knows what benefits the BSB gives:

1) The most important bonus of BSB is his ability to give re-rollable break tests to units within 12" of him - it is especially important for Bretonnian lances after the unhappy charge when the enemy charged does not break. In that case the "stuck" lance formation tends to loose a lot of it's combat power (only the front rank attacks, no charge bonus, has long unprotected flanks, etc) and might break before we can charge with additional lance.

2) The second important thing ot does is give an additional +1 to CR that is cumulative with normal unit standard bonus.

3) Thirdly - unlike our normal units the BSB can carry the most costly magic banners.

If the BSB is within a unit, he must be wielded in the front rank for you to get the bonuses he grants. Most Bretonnian generals stick the BSB in one of their knightly lances. Now - that is the position where the BSB usually meets the enemy models face to face. And that situation has it's dangers:

In many armies a character with 3+ armor save and additional wards save would be considered a tough nut to crack. But among the Bretonnian knights the BSB Paladin's armor is a softy compared to our cheapest core knights. His T4 somewhat helps - but in my opinion not enough. And usually the lance with the BSB is the most heavy hitting lance and thus is used against the hardest enemy units.

It is common practice among Bretonnian players to further enhance the BSB's ability to boost his unit's static CR - war banner given to him and/or Virtue of Duty/Discipline being the usual choices. As such the death of the BSB is an event much wished by any enemy general - his demise weakens all Bretonnian units, but especially the lance he is riding in.

Thus your BSB is the weakest link in the lance - he has the worst armor save and he is the primary target of any sane enemy. In the above-mentioned cases of common BSB upgrades if he is killed you not only loose re-rollable break tests and his +1 to CR but also the further CR bonuses that you upgraded him with. 

From my experiences I suggest the following to remedy these problems:

1) Never give cheap banners to BSB. If You want to wield a War Banner give that to Knight unit's standard bearer. The BSB can be killed and the magic banner bonuses are lost with him. On the other hand - as long as the Knight unit stands it's standard bearer can not be killed and the +1 to CR keeps working.

2) Buff up the defenses of your BSB to make him last longer (gromril great helm instead of magic banner or a magic weapon). Personally I don't favor the upgrading of the BSB's attack capabilities - usually he can be attacked by 3 enemy models and rarely can all those be killed by his 3 attacks, be they S4 or S5.

3) If You can't afford to buff the defenses then wield the BSB naked - thus it is less reason for enemy to target him specifically and he still might survive long enough to fulfill his role.