Generally Expedition is a lucky dip.
Sometimes the bases are easy and sometimes very difficult.
If you have Minotaur Chiefton you can usually use him and Cupid to destroy a base from afar.
If you have Dovekeeper you can use her to kill all the Heroes on the bases from afar too.
I use snipers (heroes that attack other heroes from the other side of the map) like Dovekeeper, Warlock, Pixie, Aries, Spirit Mage, Grizzly Reaper etc etc.
If you try to go head to head then use a tank first like Skull Knight, Dread Drake etc etc.
It really is a lucky dip as to which bases you get, your Hero skill level and normal level are key to beating it