In Chisinau (the capital), where I spent roughly a year, I would say that you hear Russian even a little more than Romanian (although there are definitely more Romanian speakers and people really like it when you try to speak Romanian). I would say the actual ratio in Chisinau is 65/35 in favor of Romanian speakers, but you tend to hear Russian a little more because the Romanian speakers learn Russian, but the Russian speakers don't learn Romanian nearly as often. The other city I lived in, Balti, has a much larger percentage of Russian speakers.

I didn't know Romanian beforehand though, so going with Russian was easy enough. I did work with some other Americans who learned Romanian and didn't have the easiest time in Moldova just speaking Romanian. They would often run into people who only spoke Russian and they had no way to communicate. As a Russian speaker in my two years this happened very rarely to me and then it was usually only people from villages and young kids (even then they were familiar with Russian and I picked up enough Romanian to communicate).

It's a very interesting dynamic in the country between the two languages. It's not as controversial a topic as some people would have you believe. People definitely like hearing Romanian more (for the Romanian speakers), but they are ok with Russian too. I got yelled at one time by a drunk guy on the bus for speaking Russian, but literally everyone else on the bus defended me and the guy I was talking too. They all knew we were Americans based on accent haha. Overall though, it's not that hard to immerse yourself in Russian in Moldova in the bigger cities, but if you already knew Romanian you would have to be disciplined because it is still widely spoken.