I only have Ghost as a 6-star tech champ already ranked up, but I have almost all 5-star versions of the solid tech champs.
Based on this tech roster, what do you guys suggest for my next R3 would be? And please state why

I am mostly utility fun instead of burst damage. All of the listed champs are unduped.
EDIT: sorry guys this should have been normally a pool post. I accidentally create a normal post. Anyways we can continue on this.
The options are Sentinel, Hulkbuster, and Ultron.