Agressive support, Blitz or Leona

probably blitzcrank, if you're a sniper with his grab then you can easily carry games, but leona's a lot easier to play IMO

leona easily because once blitzcrank misses a hook he is useless for trying to be aggressive onto the opposing bottom lane. He can still do things like flash E but he has less CC if he has to do that. Leona on the other hand is tankier since you max w and is just tankier to begin with. She has more CC and more ways to engage at a longer range and buys more time for ADCs to deal damage with the amount of CC she offers. Skillwise they are pretty even since they both rely on skillshots but leona players need to know their limits on engages more so than blitz players. Leona also triggers sunlight procs for additional magic damage with every ability she uses which can be procced by the ADC so she also just does more damage with every CC spell she lays down.

The comparison between Blitz and Leona is like...

Blitz' biggest drawback is consistency issues. He's probably far more deadly for hitting a hook than Leona is for hitting her Zenith Blade, but the biggest problem with Blitzcrank is that there's so many things that can go plain wrong using him compared to using Leona. If you want someone far more reliable, Leona is your best bet. If you're in it for the plays, try out Blitz.

Blitzcrank is probobly the least aggresive support IMO. I play very reserved and only hook when I examine them carefully and their movements in lane. It usually works out well, even against morgana, because you can either juke her out by facing her and actually pulling the adc or using your ultimate to break her shield then pulling the target. Basically if they push your lane blitzcrank has HUGE kill potential because he can just hook them under tower.

So, both of these supports are aggressive champions because their skill kits put them in close quarters with the enemy. Blitz brings the enemy to him. Leona's e brings herself to the enemy. If you want a "pick" support, blitzcrank is better at this because he can isolate and bring an enemy to your teammates and he can hook over walls. Leona requires that your teammates can follow up on your engage since you need to throw yourself at the enemy in order to land your Q (if you choose to blow your ult to get a pick off, you won't have it for teamfights that might occur in the near future).

TL;DR : Leona is a better teamfight support. Blitz is a better pick support.

Both. Depends on your ADC though. If your ADC trades well and is better in 2v2 skirmishes then you want Leona, who can jump in and CC the enemy while dealing a bit of damage while you pick them off. If your ADC prefers burst damage, take Blitz and isolate one of your enemy laners. The other will ideally be too far to help, and you'll get off enough damage on the one you pulled that if they try to retaliate you'll often end up with a kill, and if they don't then you at least won a trade and now they're lower health than you.

Depends on the ADC.

Blitz is good for the shorter range adc's, as he effectively delivers them a fresh free kill. For the longer range Adc's Leona is great as she has such peel and can even dive to help secure kills, with a way to really lock people down so the ADC's can deliver the payload.