Dubs:
+Listen to the anime in your own language
+Aren't distracted by subtitles to pay attention to what's happening on screen
+With the right casting, can be very good portrayals.
+Very accurate dialogue that is translated by professionals
+Scenes that are bad in subs can be easily turned around in dubs (The Naruto Pain scene, for example)
-Lags behind quite far from subs
-Comes in seasons, so when a new season is over, you need to wait x amount of months for it to resume.
-Hard to find on the web
-A few errors in lip syncing
-Makes no sense when jokes or plot points are derived from the Japanese language
-Some animes can be awful dubbed since the casting was terrible.

Subs:
+Listen to how it was intended to be
+Can support the anime industry by watching it through Crunchyroll or other paid anime services
+Can learn some points about the Japanese language
-Can be inaccurate at times, depending on the subber.
-Distracting during scenes involving both dialogue and action.
-Ever notice when some punctuation marks are used in subs, it makes random letters, for example "You%op3jre a jerk!" Yeah, that.