We sailed from Miami in January on Oceania which uses the same, dedicated terminal as Regent. Previously we had sailed several times on Regent from Port Everglades. Can't comment on taxis etc because our hostess in Miami drove us to the port (!). However the embarkation process was incredibly smooth compared to FLL. No computer "glitches". We embarked absolutely at the time we were told we could. And there were about 10 check in lines open. All very smooth. But the best thing is the terminal itself. Very nice. Freshly painted. Nice seats in the waiting area. And plenty of staff to "move" you in the right direction.
Miami, to me, is a huge improvement over the "cargo sheds" in FLL.