The top 3 will always be the shaman, paladin and monk. After that any random char i would like to play too. Very likely my druid is quite high since it is my herb/alchemy char so it needs to get leveled in every expansion.
Right now i have paladin, monk, shaman, druid, dk, evoker, mage, priest (62), rogue (33). Under that other random ‘gear upgrade’-chars 
My main on top. Below the class mains in random order i levelled them for that expansion. (Every class will be levelled in a new expansion after my main) Below that all the other alts in random order. Bank alts always at the bottom.
normally i havent a main so i put most used on top. In theory. Random is more accurate.
First there is my main, then all other alliance characters by level (and “importance” if they are max level), then all the horde ones with the same system.
A little ontopic question; can’t we move chars with a “gear upgrade” on the char selection screen? Or am i missing something. The order-arrows do not show up.
You can just drag and drop.
Wait what? I need to try that. Thanks.
Priests at the top, all the other crap underneath.
Sorted by fur color.
Most played/enjoyed at the top. It gets shuffled a lot some seasons, but it sort of helps me to let go of specs I’m not enjoying rn.
So my main has the very top position, then the profession army in name order. Then it’s max level palas in name order. Then the rest of the paladins in name order.
Then it works by class in alphabetical order and within that in alphabetical name order.
Ideally I’d like all my chars on Draenor now but I still have a chunk on Silvermoon (not shown) before cross faction became a thing.
Relevance of playing nr 1 — then by class.
So right now, the 7 first slots are taken by druids for me.
Theeeen comes the~~~(etc etc).
My main is my druid, so ye, thats why its orange at the top.
2nd alt is my DH, so there comes my DHs.
etc~
Oh and only 60-70s.
Everything below 60 is considered “Not worthy”, so they come behind every class (which I all have at 70) and all their class-alts at 60-70.
That’s awesome, imma start sorting mine like that.
Rn I just have mind sorted by level and ilvl relevance to the current season
By mains/level. So my mains are at the top of the 70s, then 70s, then by level.
Top one’s my main, second one’s my primary alt if I have one. I don’t care about the rest.
sorted by most loved class to least loved class, with main at the top
My main is on top, then it’s sorted by ilvl, and then by highest to lowest level
But I have ally and horde seperate. Ally first.
my main is top (this guy) then the alts i play the most are next
you name all your characters after heroes of the storm? you know theyre all in prior blizzard games?
Do not judge me 
Also there is one character that wasn’t in any prior Blizzards game.