No. Flew from Paris to Moscow and back from St. P to Paris. Although I would LOVE to do that one day. I love train travel.
Why and/or? If you're going all that way, you might as well do both. They are very different and both worth visiting. But if you're in Europe you probably have more opportunities to visit them because you're closer.
So do I, but that is one long train.
I'll be in Stockholm and I definitely want to take the ferry across to St.Petersburg, but I don't know if I'll have enough time to fit Moscow in and make it worth it. Plus I kind of have Tallinn in the back of my mind for this trip as well. So who knows.