Haste by a mile. Even for some back line caster type being able to dash, disengage, or hide every turn, with double movement, +2 to AC, and advantage on Dex Saves, is more powerful than Blur or Bless. Particularly if and when the DM lets you cheese that hide action for cover and advantage. If the DM is hiding adverse you still absurd movement to just leave the battlefield at the end of your turn and return on the next one, which, when feasible, is more powerful than the defensive benefits of Blur or Bless. And on the turns when none of the better uses of your extra action works for you you can still make a free attack with a lame light crossbow or something.
Now making Haste really shine requires leaning into a playstyle that takes advantage of it, so I can see wanting one of the others as the more playstyle neutral option. But in terms of raw power potential, breaking the action economy is always going to come out on top.
I usually avoid Haste as a spell because the "lose a turn when it ends" mechanic combined with concentration makes it extremely risky to cast on oneself, and it has too many bits and pieces to cast on a less experienced players character for them to really get the most out of it. But divorced from the consequences and with a player being able to treat its benefits as permanent class features they can actually get the hang of making the most out of I think it's pretty hard to beat.
