1st - Dagg
then rest. +12 attack is always useful; always.
I don't rank X-0DUS high due to his courage and his lack of round winning potential. T-Gaank 's solid Power and Damage are great against SOA. Dagg is the above standout, his 7 power makes him semi-prone to SOA and his attack manip is great for winning rounds and potentially perfect pilling your opponent. His damage is nice too.
Aww, come on! Where's the love for Heegrn Cr?
From an elo approach its really tough to say, personally i love x-odus for his soa, but if i had enough soa dagg would be the second choice
but t-gaank looks VERY promising, he will be great in pussycat/all star heavy elo weeks
all this being said you can fit 3 4* into 25* pretty easy among vortex
but just overally if you had just one to pick id say dagg covers all borders best, low pill fights high pill fights or just to mess up your opponent (they have to pill usually a minimum of 2 to win and then you get a pill back so it leaves them at a disadvantage)
I'm speaking from an ELO player's PoV... And it's way too close to call, IMO. They are all top-notch 4*s that have good base stats and amazing ability/bonus synergy.
X-0DUS is my first pick for many decks, but that's purely a playstyle preference. His SoA may be conditional, but his high damage makes it worthwhile -- he is a real threat and can set up KOs or unbeatable forks with ease. He works especially well with Dregn. He is also a very controlling card: the fact that you can't DR him or just beat him with a card that has a high-impact ability means you can force your opponent to play his cards in a certain order.
Looking at a DM perspective, It'd be
Dagg op, but weak to SoA and DR imo.
T- Gaank is amazing against DR and Power Reduction. Vortex is weak to All Stars. This card will murder them all, I like him alot.
X-0dus is fragile and has courage. He is nice if used right, but really, I don't like his extreme fragility and price