Tecfidera has the best relapse reduction rate of the two drugs (50% on average). The PML thing isn’t a big issue with Tecfidera because it happens only if you are JCV positive and your lymphocytes are depleted by the drug. Lymphocytes are checked every month. They are the type of white blood cell that fights viruses (which is what PML is). So if your lymphocytes are below a certain level, you are taken off Tecfidera. And your lymphocytes recover.
Also, Tecfidera works best of all if it’s the first DMD a person has taken. See Multiple Sclerosis Research: #NeuroSpeak: DMF as a second-line agent or not for information on this. (DMF = Dimethyl Fumerate = Tecfidera.)
If you find either that you can’t take the side effects (usually stomach related but these can be managed by eating the right kind of food with the drug and introducing it slowly) or your lymphocytes make it impossible to stay on the drug, or you have some other reason to stop it, you can swap to a different DMD quite easily.
By contrast, Aubagio has a relapse reduction rate of only 30%, and has an impressive list of potential side effects. If it were me, I’d take Tecfidera. And I did until low lymphocytes took me off it.
Best of luck making your decision.