What Slavic language makes learning other Slavic languages easier?

Answer 1

I would say that it depends where you start: is your native language script Latin? In that case, you should start by learning Slavic languages that use Latin script, such as Croatian, Bosnian, Polish or Czech. After that, you may introduce yourself to Bosnian, Montenegrin or Serbian (similar) which use both Latin and Cyrillic. After that, you're going to better understand Bulgarian, Macedonian and Russian.