MECIR or Instructors Rating?
I have a couple of friends who have done various combinations of MECIR's, FIR's and paid for JPA' and the like. Each have had varying degrees of success. It's all about who you train with, and how well you get along with people. Research which companies employee their G3 instructors, or go speak to the boss at the local drop zone.
It's really important to choose your training organization wisely. Very few flight schools are willing to take on fresh G3's who they didn't train. If you do the MECIR, you must accept that your first job will be VFR in a single, and that you will have to pay to keep your IR current.
If you're smart about your choices and have the right attitude towards it, either pathway can work.