Which bird is the common classic "seagull" one sees on beaches in North America?

Question

Is it the Ring-Billed Gull...

...or, the Herring Gull?

Or, could it be an entirely different gull from either of these?  As for why I'm asking, I've been curious about the different kinds of birds that live in North America.  And, for this question, I'm focusing on "seagulls".  I may do a series of "bird" questions in the future, but for now, I'm starting with this one.

Answer 1

Both are quite common in my area.  

Answer 2

There are many species of seagulls or gulls:
https://en.wikipedia.org/wiki/Gull 

On your side, two of your most known species are
https://en.wikipedia.org/wiki/American_herring_gull
around coasts and
https://en.wikipedia.org/wiki/Ring-billed_gull
in interior lands and on coasts

In Europe, one of the most common seagulls around coasts is
https://en.wikipedia.org/wiki/European_herring_gull