I first tried Rebif and it not only made me sick as a dog (couldn't get out of bed because of flu like symptoms but it brought on a huge depression very quickly. I only lasted 2 weeks. I switched to Copaxone and only lasted for 6 weeks. It made me feel like complete and utter crap. It was bad--missed work a bit. Then I went to Tysabri because that was the last resort. I could tolerate the side effects (minimal) and I haven't had a relapse in 4 years.

As other people have suggested it is somewhat of a crap shoot. Everyone's body is unique. You have to identify your tolerance of risk. You have to decide how important quality of is (some drugs are worse than
others). You have to decide how aggressive you would like to be in terms of treatment (personally I couldn't stomach the thought of a relapse).
If I had rested positive on the JC virus test I was planning on switching to Gilenya.

Anyhow, good luck! Some new drugs are on the horizon and will be out soon.