that's a really tough choice - I can relate. I had a terrible time on Rebif and stuck it out for 4 years, of which the last 2 were hell.
I transferred to Copaxone and did really well on that. Thing is though I feel myself that Copaxone took about 6 months to fully reach effect so you might not want to switch for that time period.
I am 8 months pregnant now, I stopped Copaxone this time before I conceived, but I did lose 3 pregnancies to early miscarriage when I was taking Copaxone - I will never know if they would have happened anyway or if the Copaxone had an effect.
I don't think I can help you make a decision about the 6 months window in your meds, but I would advise you to minimise the time it takes you to conceive as the less time it takes the less time you'll be unprotected by MS meds.
Things I found that helped were to buy cheap ovulation prediction tests online, we used the "Sperm meets egg" plan! - http://www.pregnancyloss.info/sperm_meets_egg_plan.htm
, and both of us taking prenatal supplements. Of course you can never tell if any of these methods do speed up conception but I did conceive very quickly.
Wishing you the very best of luck with it all,