For me its Rigard.
After more than a year of running a TC20 (sometimes 2), I’ve gotten every normal 4* at least twice. But between my 5th Cyprian, Chao and Skittleskull this purple knight still eludes me.
Hear my call if you’re out there, I have trap tools and cleric emblems waiting for you
I have four x Rigard. Wish we could exchange 
It was Rigard for me too, but he fell out of tc20 a week ago I was ecstatic 
Low on trap tools though 
Took me 14 months to finally get my last regular 4*. Skittles. 
Was planning to upgrade a second LJ, but he decided to go on vacation.
My first TC20 went into production around the beginning of July of 2018, I have since then added my second and recently (about a month ago) my third TC20 into the production. The only S1 4* I am missing is Skittleskull, like @havok333. I just hope it doesn’t take me nearly as long though.
The snipers! Magni, Lianna, Sartana, Marjana and Joon. I can’t get them though I’m playing for over 1 year and 3 months.
Boldtusk was the last standard 4* hero I pulled, which seemed fitting since Kiril was the first. For 5*s, I still don’t have Magni or Marjana - both of whom I would max out in a heartbeat.
I get Lianna once a year. I can confidently say this with my database of almost two years.
Still hoping for Magni, Marjana and Joon though
I have 3 tc20 running 24/7. magni and marjana are now mine 
Most hoped for 5* for me at this point is isnarnia followed by sartana and I would like Elkanen too, even though people don’t seem to like him.
I have 2 Rigards, but from summon gates. Been playing since November 2018.
TC13 right now, pulled my first 4* Colen. Was my 4th pull and happy. I’d love to get a new 4* Holy; just about any holy right now. Melia wants a vacation 
Rigard for me. 250 TC20 pulls and numerous summons but he’s the only 4* that has eluded me. Wouldn’t mind a Lianna in exchange for 2 of the 3 Elkanen I have.
Lianna is the one that has escaped me.
Azlar. Two accounts, lots of summons and TC20s – no Azlar.
Wu Kong. Every single 4* hero, bar Wu Kong.
(I don’t mention 5* since I’m playing since October, only 5 months - but Azlar is my only maxed 5*)
Caedmon one year and a half and nothing. I have almost all five star but no Caedmon.
I have quite a few event/HOTM heroes, but I have a lot of trouble getting the classic 5* heroes from TC20. Sartana, Domitia, Obakan, Quintus, Leonidas, Justice, Isarnia, Magni, Kadilen, Lianna, Marjana, Azlar, and Khagan have all eluded me so far. Joon would have been on the list except that he tumbled out during my Wonderland summons.
I’ve pulled every 4* except Sabina.
My only missing vanilla 4* is Tiburtus now.
Sorry to hear about Rigard, he’s probably the best van. 4* imho
Same here. A lot more than 300 TC20 trainings and still not one single fast TC sniper (however, I was lucky to pull Kageburado in Atlantis).
Also, I’m missing a 5* healer and/or cleanser. Therefore, Rigard is in 80 % of my PvP attack teams.