As you might know, I've had MS for 23+ years, and have been on Betaseron for 13 years. AT the time that I went on Betaseron, only Beta and Avonex were available. My doctor was convinced that B was more effective than A, so got me on B.
If I were newly diagnosed today, my drug of choice would be rebif, or betaseron, then copaxone. Avonex would be at the bottom of the list. Why? Because there have been several reports published over the years that indicate that Avonex might be the least effective. The discussions are around the fact that it's only injected once a week, and perhaps is gone from the system before it's time for the next shot. And maybe the interferon needs to be more regularly/steadily in the system to be effective. Or maybe there's something about the formulation of the other interferons (Betaseron, rebif), that make them more effective.
And then there's the needle size: B is injected just under the skin, a small needle, the same as used by many diabetics, who have to inject several times a day. A is injected intermuscular...a HUGE mother of a needle. Nah, I don't think so. I don't know about the other two.
At any rate -- that's what I'd do.
I've not seen any studies that indicate much difference between rebif and betaseron, other than one is injected every other day (B), and the other..what..3 times a week?
If it turns out that you really can't adjust to the side effects of the interferons (difficult at first, but manageable over time...6 months or so..for many of us...) then there's copaxone.
The GOOD news is that there's a choice. The bad news is that you're needing to consider any of them at all.
(Often the drugs are referred to as CRAB's, so as to include the rebif... )