For me in D1 it always went Warlock -> Titan -> Hunter in terms of preference. I had a hunter as they had their purpose but, whether through personal play style or something else, I never really enjoyed the hunter. It makes sense that the gaps between each class could / would expand though as going in to D1 it was said the Hunter was high agility, low armour whereas a Titan was low mobility, high armour and a Warlock was somewhere in the middle. I know that is simplifying it but to me these were never noticeable differences - they had different jumps, grenades, supers and melees but felt the same past that. They could have all been subclasses of a generic 'guardian' rather than 3 different classes. I put the vast majority of my hours in to my Warlock but I never felt quicker and squishier as a Hunter or slower and tankier as a Titan. I didn't play the Hunter or Titan in the beta but if they have exaggerated these differences then I am for it.