Replace dental bridge or go with implants? Currently have a 3 unit bridge for teeth #3, 4 & 5 (missing tooth was #5)

I had a 3 unit bridge replaced in April 2012. Just 15 months later the abutment tooth cracked under the bridge (tooth#3). Apparently this tooth previously had a root canal done on it & now it was cracked. My dentist said tooth #3 has to be extracted and referred me for a consultation for implants. Per implant dentist, I would need a sinus lift and bone and veneer graft to do implants on #3 & 5. Would it best to replace the bridge with a 4 unit bridge or complete the sinus lift and do implants?