Active noise canceling actually does not block noise as well as let's say, the DJ style headphones that are like a vice on your head nor do they block noise anywhere like excellent in-ear types. However, with music on, a good pair of active noise canceling headphones are excellent as you will not notice outside sound and with the benefit of a more comfortable fit (usually).
Etymotics on the other hand are hands down the best for isolation, however, their sound is something that one must become accustomed to and sometimes folks will never get accustomed to them. They are also not the most comfortable since they do go pretty deep into your ears. Ok, REALLY deep. They also lack bass impact, yes they hit the bass notes well, but there's no impact thus you are going to lose a lot of body from your music (thus the reason many never become fond of the Etymotic sound).