its funny that people are saying its hardest to fight katana with shielder. imo its the opposite, katana is useless vs shielders - unless they are very bad, you can't fient/chamber a decent shielder like you can a manual blocker, so you just have to hit shield 50 times  
. longer weapons and backpeddle is a much  better counter to shielder imo. katana is basically a 1h without shield and worse animations - so I find shielders complaining about fighting it very ironic  
.
Well I can fight pretty much any other class and feel comfortable I have a good chance at winning except when some guy with 8 athletics come zooming up at me and swatting at my shield with his stick faster than a fly blinks.  It's not katanas that are hard to face, but agi characters with high wpf and decently fast weapons.
I will face shield breakers all day.  Hell, I love fighting mauls/long mauls!  I think its fun and I win much of the time.  But those "ninjas" are the tricky ones for me.  Not impossible, but a pain in the ass.