As SGT said, each DMD comes with a different autoinjector or machine. Which DMD have you chosen? If it’s Rebif, then I can vouch for the Rebismart - it is easy to use, you don’t need to even see the needle if you don’t want to and the needle is very fine so it hardly hurts at all. I used to be on Copaxone and I didn’t like the autoinjector so I manually injected - it was much easier as I had more control. This was a couple of years ago now though, so they may have improved the autoinjector.
As Daniel has said, the more important decision is what DMD to choose rather than how to inject it. How to inject it may be a factor in your decision, but things like frequency of injection, whether it’s subcutaneous or into muscle and side effects are probably more important. The msdecisions website is a great place to get info if you haven’t chosen already.
I went for Copaxone the first time because there were no “flu” side effects and it was subcutaneous. When that stopped working for me, I went for Rebif as it gets the best results in recent research. I opted for the Rebismart machine because it has a reminder on it and tells you which bit of your body to inject into - both things I doubted my memory would cope with as it isn’t an every day injection!