Hello Grab, This is very simple Microsoft's MSN is very old service and having updated gradually and launched after long time. I think MSN is best between them.
If I remember correctly, the MSN search runs through Bing, so MSN is nonexistent, only the name remains for the sake of recognition.
My dear friend, Microsoft's Bing and Microsoft's own MSN are same. Both used to give the similar result. Only in few cases it may varies but other than its pretty similar
Bing is a real time search engine using different algorithms to MSN. The background data is the same, but the results differ. I prefer Bing as it's got rid of the clutter of news etc - not trying to be a portal, just a dedicated search engine. The preview option where you mouse over the link is excellent in bing, and something others could learn from. So, in my opinion, Bing is superior as it's based on real time finds - is less cluttered - and offers better information before you click.
I hold the idea is that MSN is just so son. While wheather bing is good or not, I do not know, since I did not use it before.