I've started travelling a lot in the past few months with a job change and as a result I'm trying to familiarize myself with levels, MR's, a ton of terminology etc.

My primary plan is with Alaska Airlines since I fly their destinations frequently (and their large NW presence) but I'm curious about a secondary mileage plan and whether the value is with a partner of Alaska (such as Delta or AA) or with another carrier entirely (like United)? Or do you stick with the one plan and not worry about the others?

I would like to travel internationally this next year while completing a few MR's and wondering what the prevailing opinion/advice is?

Thanks!