1 thing for sure: A is getting stale. jump whether you have counter offer or not and don't look back.
if you like overseas, go for B.
C is very aggressive, which can be bad or good depends on how you look at it. they desperately need people, probably someone else felt lousy and left. from the looks of it, be prepared to be pressured, busy and work OT. if you are really interested, you can negotiate a higher salary at C.
these are my opinion and i hope you will find other ways to look at it to get a clearer picture.