Crunchyroll has a variety of animes but you have to pay to access content from mobile and streaming devices.
Hulu is a great service for tv shows but it is somewhat lackluster in anime and ads do get annoying. You also need to pay to view from mobile or streaming devices.
Kissnime is one of the leading site that host anime the day after it airs in Japan. Otherwise ads are a bit annoying and videos are block if ad block is detected.