I think סנדביץ' is far more common, at least around me. כריך is more common in writing. But maybe in some linguistic communities the word caught on better, I can't say.
the word sandwich is in use in Hebrew, but it is a loaned word (BTW, @AlmogL the Academy stated that sandwich should be writen סנדוויץ' with וו, not ב). So technically sandwich in Hebrew is כריך. Also, people tend to use סנדוויץ' to describe a general sandwich (for example, "יש לי סנדוויץ בתיק, אם אתה רוצה" - "i have sandwich in my bag, if you'd like), and כריך when they describe a specific kind of sandwich ("אני יכולה לקבל את כריך הגבינה בבקשה?" - "can I have the cheese sandwich, please?" or "מה אתה רוצה בכריך?" - "what do you want in the sandwich?").