Hmm, I don't know where I stand on that one, on one hand MS Equation is better being click and play because it's easier to learn, there again I also like OpenOffice.org Formula as typing is so much faster than clicking!
Overall MS Equation is better not because of its interface but because it has more features like multi-line and more symbgols are supported. Don't be fooled though, MS Equation isn't an MS invention, they bought it from another company called Design Science.
Also note that with OpenOffice Formula you don't have to remmber all the syntax, you can click on the buttons. To be honest my ideal formula editor would be Latex with a graphical front end so you can choose whether to have a GUI like MS Equation of a pure text interface.