Currently Russia presents an ethical dilemma so its not on my list. I did visit Moscow about a decade ago and it was interesting.
Crimea is probably "safe" especially if you are not a US Citizen. Still, same ethical dilemma for me.
But I did return from Odessa in September and enjoyed it immensely. Is it safe? Sure, until it isn't. It is primarily a Russian ethnic city and as such it is under a lot of pressure from Russia to join the revolution against Ukraine. The one attempted uprising was brutally crushed but it could happen again. Also the Russians are putting pressure from both Crimea and from the lands they have illegally invaded in Moldova; and Russian war ships sit off the coast. So the Ukraine Black Sea coast is pretty boxed in right now. Putin even describes the region as being part of his New Russia. So there is no pretending about intent here.
Personally I love Ukraine, but preferred Kyiv to Odessa. We will be back in Kyiv in the spring I suspect. If you are looking Black Sea Coast then check out Varna, Nessebar and Burgas in Bulgaria. All equally excellent (my favorite is Nessebar)