General

Shields and Secondaries are still slightly different, even though they can both achieve weapon potentials now.
They didn't remove all the old, junky lines that shields could get before, they just added all the weapon potentials in on top of it all, so there's more junk lines to be had on a shield vs a secondary.

@leopard16: Any shield that's 100+. I wouldn't use secondaries as you can't scroll them.

[quote=leopard16]is it bad to use that white bishop book? level 100[/quote]

Not at all. The white bishop book can achieve the same potentials as the shield and is less expensive.
You don't even need to bother scrolling it compared to a shield.
The loss is that you CAN scroll a mage shield with Shield for Magic ATT scrolls.
This means that shields on mages can have a greater potential for a higher boost in damage than secondary weapons.
Shields are more wanted as well since 5 mages can use them, especially tradable ones like a VIP mage shield.

[quote=nhan1st]Use a VIP mage shield, or at least a last UWG one. It;s way better.[/quote]

is it bad to use that white bishop book? level 100

Thanks for the tip.

Use a VIP mage shield, or at least a last UWG one. It;s way better.

It's what @allovershoe stated. To get any sort of % boss on a shield, the shield itself has to be at least level 71. However, to get the most % boss per line (40% I think it is) possible you need a 100+ shield or secondary weapon.

I believe only level 71+ equips can get % boss :o

[url=http://www.basilmarket.com/MapleStory-Potentials-and-Miracle-Cubes.html]MapleStory Potentials and Miracle Cubes[/url]
I believe its outdated but it shold be enough to answer your question.