It's a tough choice for me.
On one hand, Leon and Helena's part looks like it's going to take place in the White House and if you know me then you know that I like missions where I'm in the White House (No matter what kind of version it is) because it's not use in games most often and I usually find those levels to be my favorites most of the time (Well consider it all the time since I've only played 3 games where you had to go to the White House and I enjoyed all 3 levels in those 3 games.), then there's Leon who is my favorite male character in the series and I like how Helena looks, and it looks like it's going to take place in the most places from what I've seen.
Then on the other hand is Chris and Pier's story and from what I've seen the China level looks really fun.
And on the last hand is Sherry and Jake's story, and while I haven't seen barely anything from it, the place that I saw in one of the trailers looks pretty interesting, then there's the fact that Jake is the son of Albert Wesker and I want to see how he is like (Gameplay and character wise) and then there's Sherry Birkin who looks really cute, and from what I've heard, Jake is supposed to play a lot like his father.
More than likely I'm going to start with Leon and Helena's story first, but that is just a maybe because I still really don't know which one that I'm going to try first. But more than likely I'm going to go with Leon and Helena's story first because there is a lot that I like about what I've seen and that their story seems to be strongly tied to the mystery woman.