Evan Peters was my absolute choice for The Flash.
I've always imagine Barry as a very intelligent, articulate, mature, confident and optimistic guy in his mid 20s. I wanted his actor to look relatable, charming, light-hearted and yet very sloppy, awkward and disoriented. And that's exactly how Evan Peters looks ! Plus, he's a good actor, he has improved himself over the years and thanks to American Horror Story, he has a lot of fangirls and fanboys. But since he was cast as Quicksilver (the irony...

) for what will probably be a brief and useless apperance, I guess it will never happened.
I'm pissed. Anyway.
I'm such a big fan of Aaron Paul. He is a phenomenal actor and I hope he becomes a big movie star in the near future. I can't quite picture him as Barry or any other superheroes, but I would be so happy if he was cast... even though he's 5' 8"... and older than Cavill...!
Ryan Gosling would make me happy too (even though I want Barry to be the younger member of the JLA), but he takes his career way too seriously. He'll probably never portray a superhero in a multi movie franchise. Let's move on...
To me, Sam Claflin PHYSICALLY looks like a pretentious prick full of himself. But he's a good actor, he is a young rising star, he looks the part and he could give some edge to Barry,
or ruin the character by making him look like a *****ebag, ala Andrew Garfield's Spidey 
. His casting would be a good news imo.
HOWEVER. Even though I looooove Arrow and I really liked Gustin's performance, I absolutely don't want Arrow to be a part of the Man Of Steel Universe. It would be a dumb, lazy and cheap move for WB, IMO. I wouldn't mind if Arrow was a HBO/Showtime/FX/AMC type of show with a bigger budget, an impressive artistic direction and a more prestigious cast. But it's not, AT ALL. Arrow is a CW-show, with serviceable actors and a cheap budget. It's AMAZING for what it is, but it does not belong to the big screen.
A lot of people think that having two Barry Allen at the same time would be confusing. But for who ? The majority of the general audience have probably never seen a single episode of Arrow and a lot of them probably never heard of it. They will be just fine !
Anyway, don't to be too harsh on me, it's mt first message ! Also, I'm a french guy so please excuse my english !