I am a Zoom Player user, but the main 3 reasons I ever preferred Zoom Player over MPC, was how you could set Zoom player to play the next media file in the folder, without having to create a playlist for it to play the next file, the ability to zoom in and out the video/window with the mouse wheel and the fact I found a skin that let me shrink the player to the point the window was really tiny, making it perfect for any multitasking work. I also used the shortcut SHIFT+H which would bring the play history in it's nice sleek interface, but that's secondary.
For better or worse, Zoom Player looked better too and all nice, but no matter what, unlike MPC, it did not like external Codec packs. Also after testing for a long time I came to the conclusion that ZP uses more sources than MPC, so MPC is indeed more lightweight.
For anyone that does not like the windows 98 look of MPC, I suggest to look up KCP Codec Pack Black Edition. It is a codec pack compiled to support extra codecs packed with the black edition of MPC, which looks really awesome. If you want to see an image of how it looks if you tinket a bit with it's looks, here it is on my windows 7 machine;
The buttons on the top right do not appear until you move your mouse over there and then they pop up. So do not worry, you won't be watching your movie with these there.