Yes, Super Mario Brothers is amazing. I believe the reason it's so successful is because anyone, no matter what their age, can pick up the game and have a great time. I think that's the sole idea Nintendo has always tried to work from. Look at the Wii for example. I think that's why the Wii is becoming so successful.
My favorite Mario game is definitely Super Mario World for the SNES. I still, to this day, get that game out and play it. And when they remade it for GBA? Oh, man, I about died and went to heaven. Portable Super Mario World FTW!!!

And yes, I don't care what side of the gaming fence you're on, Nintendo will always be the best. If everyone would take off the fanboy-shaded sunglasses and look at the facts throughout gaming history, no one could really argue otherwise.