>What class or subclass do you most want to see redone?
Depends on what you mean by redone.
Rewritten from the ground up? 4elements monk. No contest.
Revised more like Rangers? Warlock. I like the direction, but it has so much untapped potential. It should have more clear progression and options in Eldritch Blast, which should be a feature that scales with Warlock level, and works off whatever pact you have. I always felt like EB, as it is now, should have been tied directly to the pact boon.
>Blade Pact lets you make x amount of attacks with the weapon die and strength/Dex + EB damage, where x is the amount of missiles the EB would make according to your level. Raw power, and none of the utility effects.
>Pact of tome is more or less like now, with the movement and field control abilities it has. Power as the EB has now, but with a ton of utility.
>Pact of Chain let's the Warlock attack directly through the familiar, letting him potentially not even be in any kind of harm by not even being in the same room. Alternatively, EB can only be used as a bonus action, and casts through the familiar, freeing up the action to use on another spell on the Warlock spell list, creating a better synergy between them.
Invocations should not have anything to do with EB. They should be more or less like they are now, but mandatory ones should be folded into the pact boon (extra attack, Cha damage, rituals, etc) leaving just the flavourful options like Disguise Self, beguiling influences, Eldritch Sight, etc. Possibly with slightly reduced invocations, especially at lower levels, so we don't get all the multiclassing cheese.