I have had a few iterations of Shure earphones, but I almost got Etyomtics each time.
They aren't actually noise cancelers (unless I am not aware of the ones you are looking at). Noise cancelers are active devices that monitor ambient noise and do their best to emit ambient-noise-canceling waves. As an audiophile, I don't like crap added to my music, so I think you are making the right choice by going with a passive, noise blocking earphone.
Etyomtic's and Shure's earphones simply (and extremely effectively) block ambient noise. They are like earplugs with outstanding microdrivers in them. The more expensive ones also have amazing (IMO) frequency response, as long as you get them sealed with your ears.
Some people find them uncomfortable for extended periods. They aren't uncomfortable for me until I have been wearing them for, just a guess, around 5 hours.
I have had the Shure E3c and currently have the SE420. I actually preferred the comfort of the E3c, but the sound is comparable. I would say the Etyomic ER-4P is similar in performance to the Shures I have had.
I wouldn't go with any other brand besides those two, personally. If you have the $$$ you may also want to consider the Shure SE530PTH (
Push
To
Hear), which, in an office situation may be nice: it would allow you to click a button and allow you to hear your surroundings.
EDIT: If you have the cash, you can have an Audiologist (I think that is the right term for ear-doctor-specialist-guy

) make a custom mold of your ear for high end earphones that will work wonders with getting the perfect seal. I haven't done this, but I imagine comfort could be increased quite a bit.