Quickest way to identify line wire and load wire in a multiway switch
Every 3-way switch has two brass screws, and the two traveler wires always go on those.    They also have one black screw whose name is common, and either your always-hot or your switched-hot wires will go on those. 

Every 4-way screw has two brass screws for two travelers inward, and two black screws for two travelers outward.  Every wire on a 4-way is a traveler.  

This means in an entire 3/4-way complex of any size, every wire is a traveler, except two.   Those are always at 3-ways, always on the ends, always on black screws, and are always either always-hot or switched-hot. 



If you're fond of not losing your mind, I have a suggestion.  I work in conduit with individual wires in my choice of color.  I use 2 yellow wires for travelers*.  Travelers are interchangeable, and there is no need to distingish them from each other, though it sure helps to distinguish them from other wires.  Two identical odd-color wires running together are quite distinctive.  If you're not in conduit, you are stuck with black white red for everything, but you can mark them with colored electrical tape.  They sell 5-packs of colored electrical tape for $3 in a lot of stores.  I'm fond of yellow for travelers, green** and blue for alt-travelers if two separate sets are nearby, red for switched-hot, black for always-hot and the law already requires neutral be white.  (But white can be anything). 

* If I have several 3-way circuits in close proximity, then I'll use purple, blue, etc. for the others, again in pairs, it's quite distinctive.)

** Small wires cannot be remarked with green tape to be a ground.  So it changes nothing; the wire is still a hot.