Hi Sasha, IELST and TOEFL are two well recognised exams. IELTS is more British and TOEFL is American. Most universities and companies accept both. So I would say which ever :)

None will be good enough absolutely everywhere. Some institutions require IELTS, some TOEFL, some one of Cambridge certificates. It's only your choice depending on where you're most likely to use it. IELTS an TOEFL you basically can't fail as it is as you'll get a certificate anyway everything will depend on the band and points stated in it. Those 2 are only valid for 2 years. FCE, CAE, CPE can be failed if you don't achieve the minimum number of points but the certificates are valid all your life.