from what i remember supercollider is more like a programming language (see also Chuck, CSound), whereas Max and PD are completely visual. theyre pretty much the same thing but Max is probably better.
reaktor can do an awful lot these days and has amazing sounding oscillators and so on (basically like the best NI softsynths).
compared to reaktor Max/PD require more work to make things sound smooth, you have to have a fairly good idea of how things like this work, whereas in reaktor its much easier to just stick together things you are familiar worth. something like making a granular synth that sounds as good as the reaktor one in Max is a hell of a lot of work.
i'd suggest trying the Max demo, its quite generous in what it lets you do and comes with lots of example things to play with.
Don't forget AudioMulch either. All of Four Tet's music is made and performed with it.
if you're interested in the coding stuff check out Chuck.
being a coder i found max intensely frustrating because you end up having to do things you could easily code in a minute in a really convoluted way to fit how max works