It depends on what your priorities are of course, but I think Draco is probably the best overall champ in that list. Though Nethril and Miscreated Monster aren't far behind and should also absolutely be 6*. The others are also decent picks for sure. 

As a free to play you must be one lucky SOB!!  Draco is amazing, particularly for CB, Scyl is great in a number of different places, and Kymar is great in arena!  You will likely need Apoth at 60 and MM too, they are just too useful across the board.

Man I wish I had Draco...  :(

Who are you using as your Campaign Farmer?

I was lucky to get Draco early in the game.  He is a monster.  I have him geared for CB but use him in every type of battle.   Full ascension and full masteries.  You wont regret it.  

Kymar

I'd go Draco then MM. MM I use in nearly every dungeon. After that, I would say Apo.

Kymar as a Campaign Farmer?

I would have never guessed.

How fast does Kymar beat Campaign?

Ive managed tp three star all the way through brutal fairly quickly nightmare though is where he comes a bit short without a strong tag mate

Draco

if anyone tells you Candraphon don't listen, he's getting nerfed soon and we don't want another Rotos

Does anybody suspect that Plarium gives paying players better pulls? I'm a cas player who is not going to plop down big bucks on the game - I've been playing a lot for 3 mo now and my pull have been terrible. The best champ I've go is Kael that I started with. All my Epics except Aothar have been crap and 90% of my rares have been bottom of the barrel. And of course bubkis on the Legos. So when I read about folks pulling 2 to 5 legos and killer Epics and Rares in a few months, make my head want to explode...I'm like WTF?