One of my favorite names/pairings is LaurA Elizabeth. Sarah is one of my favorite names as well, but I do not think it flows well with Elizabeth (the double vowel at t he end of the first name and start of the middle name), so I vote for Lauren Elizabeth (though, I think Laura flows better).
Laura Elizabeth is the name of Laura Ingalls Wilder, by the way. I am not sure if that would make a difference to you, for or against, when considering using the name Laura Elizabeth or Lauren Elizabeth.
EDITED TO ADD: Someone referenced Clifford the Big Red Dog, that character's name is NOT Sarah Elizabeth it is Emily Elizabeth.