Ah, a fellow 100 Rep chaser! Congrats!
I love being Esteemed!
That being said, my fav ground mount will always be the Bloodfang Widow.
~https://cdn.discordapp.com/attachments/473825485311180800/606093638388154369/WoWScrnShot_121616_104813_-_Bloodfang_Widow_acquired.jpg~
Yeah all 8 pixels look fantastic 
I’m think the Tomb Stalker, Midnight 2.0 and all three infernals (red, green, blue) look amazing. Updated graphics, cool colors and a lot of attention to detail.
Mekgineer’s Chopper, of course.
That’s nice, its still the best looking mountain in the game to me.
Argent Warhorse is still one of my top go-to ground mounts after grinding it out in Wrath. It has a great, serious color-scheme, is useable by either faction, and it basically lets anyone ride the 'ole Paladin mount. It also has the nice, steady gait of the horse mounts. I mention this because, while the Saber-type mounts are cool, they don’t feel fast because of how they run.
Second choice is probably Kael’Thas’ White Hawk Strider (substitute Void Strider for Alliance - its “galaxy” bits are too cool). It’s pretty. It reminds me of an epic time in my WoW experience (BC). And Hawk Striders have a nice gait as well - they feel fast, though less steadily than the horse mounts.
Overall, I prefer small mounts as being smaller models and closer to the ground gives the illusion of greater speed. Bigger mounts feel like yachts or Cadillacs .
That is really easy… Magic Rooster Egg is way better.
Running Wild 
Oh that’s a good one.
That, brawler’s mushan, and the fox are my favorites.
Oh and running wild <3.
Meh, I think Stormpeak has the prettiest mountains.
Magic Rooster, how is this even a question
I have wanted a palomino horse since I very first started playing and saw one tied to a hitch post. But those mounts are unavailable. 
However, this one is:
I will have him, some day.
White war talbuk
Scrapforged Mechaspider
Snapback Scuttler.
I think I’m close to 1000 attempts for that one… /sigh someday.
Junkheap Drifter
Got him last nite.
https://www.warcraftmounts.com/mounts/kaldoreinightsaber.php
But I ride my Pureheart Courser a lot.
Came here to say this. Spider is best.
And I have severe arachnophobia. Riding around on him is a sort of therapy.
Plus he looks damn good in shadowform.
~https://i.redd.it/1pnxhl6pm1x21.png
Those pvp coursers are nice looking mounts.