Simple as that: triple AXP from regular moobs, nothing more.
I can tell you how long it take to get lvl 30 already, comparing to other gainings in XP. If you don't farm ARID, or - more! - you want to gain some AI levels before hitting 200, it takes:
: from 15 to 30 AI level 85 days, doing 1 daily per day
: killing 12000 aliens*
* aliens tend to have lots of HP at past level 200, and soling them is asy, but timesinking.
I would like to have a chance to speed it up with team (not solo!) and there is no better place then LE missions.