For me, any confusion between the two in terms of spelling, etc is irrelevant because where I live (New Zealand) the two names are pronounced differently.
Sarah is SAIR-ra and
Sara is SAH-ra. I much prefer
Sarah. Maybe it's a bit overused (in my year group of 80 girls at high school there were three Sarahs) but that would never stop me from using it, I love it too much. I think it's the sound that makes me like
Sarah better,
Sara sounds a bit like you liked
Sarah but wanted to be a bit different (and posh), although I like the way it looks more too. It's also the image - I feel like
Sarah is really adaptable and is a name that fits a wide range of people, but
Sara is a bit narrower. I don't think
Sarah will be dying out anytime soon, it's pretty classic. I like
Sara too, but have never met one. I like
Sarai, but find it a bit clunky, and I love
Zara (which is ZAH-ra here, don't know about you).