Routes between SE Alaska and Seattle, Seattle and Anchorage, as well as intra-Alaska routes bring in a lot of money for AS. I would say those three types of routes are the most profitable, in that order. The profits from Alaska help to off-set the cost of competing with WN and UA in the lower 48.
SEA-LAX and routes to Mexico are also profitable, although not quite at the level of the others mentioned. Aircraft going to, and coming back from Mexico all get bunched up at the beginning and end of the day, so load factors are sometimes low on early morning SEA/PDX-LAX flights and evening LAX-PDX/SEA flights.