Western Slavic Languages

Most of us know that this includes Serbian, Croatian, Slovenian, and Bosnian. I know that S/C/B are very closely related, but the question is how related are they? Are they close enough that if I learned one would I understand the other ones rather well, or are they just mutually intelligible, and learning one would get me by in the other countries? If so, which one would be the best to learn. In an example, they say that Norwegian is the middle language, it shares vocabulary with Danish, but phonology with Swedish. How is it with West Slavic languages? I'd like to know, because learning one seems pretty attractive if it's 3 for 1.

>Are they close enough that if I learned one would I understand the other ones rather well,

Yes, apart from Slovenian, that's a little more different than the rest.

>or are they just mutually intelligible,

For the most part, yes. Some word differences, nothing amazing.

>and learning one would get me by in the other countries?

Definitely, but would probably get you kneecapped.  It is 3 for one, but you need to understand the... tense sociopolitical climate between all three.  Honestly, you're about to start walking blindfolded into a minefield here.