It seems that the ExCPhT is more geared towards community practice whereas the PTCB has a broader approach and encompasses hospital settings as well. I've honestly never heard of the ExCPhT and I would definitely recommend you take the PTCE if you are thinking of becoming certified just for name recognition alone.
They are both NCCA certified but I don't think all organizations will recognize both. The ExCPhT is endorsed by the National Community Pharmacists Association (NCPA) and the National Association of Chain Drug Stores. The PTCB is endorsed by the American Society of Health System Pharmacists (ASHP). Just by endorsements alone you can see who each test is geared towards.
The ExCPhT tends to be a little cheaper to take and used to be the only test offered on demand but both tests offer this option now.
TL;DR
Take the PTCE for name recognition.