Veigars rework is the best one so far.

I really enjoy playing him now.

I no longer feel like I am just a walking nukebot and I feel like I am being rewarded for actually hitting spells, rather than just throwing out spells my enemies can't possibly dodge or do anything about.

I can also stack AP much faster or harass the enemy laner while doing so, which feels awesome and rewarding.

And Event Horizon is now a cool ability that requires some thought, rather than just using it when the enemy is on the edge, giving them no way to escape a certain death.

Dark Matter is no longer a sure hit all the time, yet still hits extremely hard when it does and it rewards the player for doing so, which feels accomplishing and also has reduced cooldown and mana cost, making it a great way for Veigar to clear waves when behind.

Primordial Burst feels as cool as always, it's a shame it's not a Skillshot aswell, this way it could have some utility strapped on it too, like being able to secure Objectives with it, but it's cool nontheless.

Veigar's rework is the best one so far and I wish they did the same thing to Annie. Especially with Pyromania.