Depends entirely on my character (and sometimes transmog). For my Mage (this character) I think I will always use “the Insane”.
For my Warrior I like using the Knight title with the BFA S1 Elite Glad set. Crusader for my Paladin. Deathlord for my DK.
For my Hunter I use “the Horde Slayer” when I am using my R14 armor set.
Title–Knight of Feathersworth for collection of 1800 Unique Battle pets…very few have this title now…
As a Vanilla Vet, I used to rock First Sergeant 24/7 before they added the PvP versions since it was one you couldn’t get any more.
Other than that I will generally use Blood Champion if I’m in the mood to use my red Xmog.
If I’ve decided to switch up my mog I’ll go with one that’s thematic with the color scheme .
Otherwise my default is usually Elder or Matron (again to reflect the fact that I’ve been playing since Vanilla).
My paladins usually get the Crusader title, though my Blood Elf Paladin will also rock the Blood Champion moniker.
For my DK, I pretty much stick with Champion of the Frozen Wastes.
Blossom Bringer tends to be the go to for my Resto Druid.
And my herb+mining and old content speed running toons get Farmer for obvious reasons.
My priest has “the Dreamer” because it fits her. My lock has “Seeker of Knowledge” because it fits her but also because I put a LOT of time into getting that achievement and I want people to see it lmao.
bloodthirsty or the insane on most light bringer on my pally because it fits best
i appreciate the thought you put into it
She’ll pretty much forever be the Butcher because her namesake (a character from a book) has the alias The Butcher of Caprile, so it fits the theme too perfectly to pick anything else.
The title is from Ashran though so I technically can’t use it on any Horde alts with the same name. For those I usually go for alliteration: Malicious or Merrymaker or Matron or Minion of Mayhem.
Breaknecker because it suits
Hand of Adal, i guess i remember seeing people with it in BC and thinking they were serious, like you’d see someone on a ZA bear with the Hand of Adal title in a PvP situation and give them a wide berth lol
Not that it has the same feel it once did, i guess i just like it because it’s old now so there are fewer and fewer of them around 
Cataclysm Enthusiast to show everyone how much I liked Cataclysm
Birdwatcher to show everyone how much I like birds
no title. it’s cleaner.
I think my “Jenkins” has gone missing , but I liked the " jenkins" cause it annoyed purists.
Right now, The Real Deal. It’s really goblin-themed, and I’m real darn happy with myself downing Underpin ??.
I may switch back to “the Smoldering” since it’s also pretty fitting or a goblin, and my highest performing M+ season.
I have a character named zovaal, so he put on shadowland enthusiast title
another character i have wear the scarlet crusade tabard with title inquisitor
Lord of War because it’s sexy
I use the title from the Venthyr “Count” because I love the idea of “Count Cursewords” - makes me sound like a foul mouthed Sesame Street muppet
It also sounds like a command. Count how many curse words there are lol
Also:
Depends on the mog i’m wearing for the week. This week i’m gonna go with goblin themed rocket stuff to go along with “The Explosive” which i got recently from 20 Cartels of Undermine Renown.
Trashmaster, is the reason not obvious?