I've struggled w/ this same question ... and have decided that getting less breastmilk for a long time is better. Don't ask me how I formed this opinion.
BM for a longer time because it aids digestion. I've always supplemented and saved lots of what I pumped. My pedi and home health nurse both said even 1 bottle of Bm a day aids digestion and will prevent constipation.
Re: Opinions on Supplementing
I think better is hard to qualify.
Me personally, I'd choose to suppliment and bf for a longer time. I have nothing to back up why I'd choose that, though.
I would go with less BM for longer. Your LO is still getting the goodness of BM even it is less than normal and that means more protection for longer.