Sona q = damage e = speed w = heal Yuumi q = damage e = speed+heal w= invincibility :(
Their ults are similar I suppose but I feel like yuumi doesn't have to worry getting all in'd
Which scenario is better to pick sona/yuumi ?
she is not. her play style and effect on your team is whole different thing
Sona does more damage? Sona can buff her entire team? Sona's ult is instant unlike Yuumi's? if you want to say that they are both similar then fair enough but so are many other champions in the game. Sona and Yuumi are very different even with kits that do similar things
Sona is for 5v5 team fight. Yuumi is for hyper mobile solo carries.
Yuumi is also good at preventing the enemy team from making picks / assassinations since all of her healing and speed buffs go onto one individual at a time.
Idk why people are downvoting, because you're right. Both are terrible in lane and have super weak heals, until they scale super well. Sona can be more independent though and sort of a playmaker once she scales (although she is best in teamfights). Yuumi can't do anything by herself and will always be reliant on her team. They're also very poke-oriented in lane, and can only handle all-ins after 6.
The only times I'd pick Yuumi over Sona is when you have an adc who doesn't have to all-in, like Ezreal, Sivir, or Caitlyn. She can also be good with bruisers or people who dive into the fight, where Sona is too squishy to follow.
Sona Also has Better AP Scalings, Better Base stats aside from Movement speed, Health regen Sona also Has Hard CC Which is Stun, which is instant. While Yuumi only snares after 3 hits. Sonas Q While more unsafe, is Undodgeable if She does use it. Both Very Fragile
Yuumi feels like a safer Version of sona but weaker in almost ever other regard.
Sona is strong, very strong. Its just shes just very unsafe and fragile.
she is much like Sona on paper,
Yuumi is a harder support then Sona in the sense of Yuumi relies upon her team way more then Sona or any other support for that matter, Sona unlike Yuumi can carry and is far better in a fight when alone then Yuumi but Yuumi is far superior in a 2v2 and can offer things that no other support in the game can "try 
and 
on her" but if her team sucks she really can't do much.
in the end, Yuumi is a Sona who plays favorites and in my opinion Yuumi is the best support for jungles and tanks.
