Is Shyvana better with a comp with high CC, and Vi with a comp that has high all in potential?
Like if I had a Riven top and Yasuo mid, I'd pick Vi, right?
And if I had a Lissandra top and Annie mid I'd pick Shyvana?
Is there anything on the enemy team I should take into account when deciding what to pick?
If enemy team has a strong peel tank like 
and a high priority like 
then Vi is probably better.
If you just want more total damage and general wreck it ralph-ness (like if they don't really have their damage focused on 1 person, but several dps or bruisers) then shyv probably wins out with her higher tank stats and damage and her damage is a good mix of physical and magical so it's harder to build against. She's just easier to kite and peel off high priorities making it possible to make her completely useless if they end up being good at 'protect the carry'.
So tl;dr- Shyv is probably 'better' or more overall useful, Vi is more of a niche pick when you specifically have someone you want to lock down and don't want anything stopping you from doing it.
Vi is better at ganking difficult targets and counterganking, while Shyvana is better for farming and counterjungling.
If the enemy has a squishy backline damage dealer ( 
) then 
is definitely the way to go.
Other than that, they're pretty expendable.
Vi is who you pick if you want someone to lock down and get to high priority targets ( ) while shyv is who you want for basically the same reasons you get a Jax, pure bruisery power.
