Phone Call: Message demanding an immediate response or an extended discussion
SMS: Short messages demanding attention ASAP but no significant discussion
Hangouts/IM: Short, time-relevant but not urgent messages
Email: Long, important, but not immediately urgent messages
LJ: Long/rambling and undirected messages that I don't really expect a response to.
Paper letter: Birthdays, Christmas, and social messages to/from my grandparents.
Consequently, I have my phone set to make noise for calls and SMS and just flash for IM and email.
Google's integration of SMS into Hangouts has broken this in a way that I cannot fix without tracking down and nagging every android user I know who has my cellphone number in order to get them to either 1) disable SMS in Hangouts or 2) manually split apart my email/phone contact book entries, so that their Hangouts app stops sending me SMS messages. This is actually impossible in some cases--e.g., my mother, who would have no clue how to do this.