Circumnavigation

i think west to east is the longest distance, followed by south to north, east to west with north to south being the shortest distance of all

Correct. The earth bulges slightly at the equator (due to the spin I seem to remember).

fresco is right. The earth isn't a perfect sphere, it's a somewhat flattened sphere due to the centrigual force of the spin. It's got the planetary equivalent of middle-aged spread or a beer belly, thicker around the middle.

Incidentally, if you're thinking of circumnavigating the earth, here's a circumnavigation question for you. Let's say, while you're circumnavigating you trail a wire behind you. (It floats on the top of the oceans). You're pretty sure you have just enough to go completely around the earth, but you get to the end, let's call it 25,592 miles around, and you find your wire is just a yard too long, so you figure, heck, a yard in 25,592 miles, I'll just solder the ends together and spread it out evenly, and no one will notice. Let's say the wire is stiff and springs away from the surface when the extra is fed in. How far away from the surface does that extra yard make the wire spring? A millionth of an inch? A trillionth of an inch? Uh, uh.

There's an equation to calculate the answer to that problem, but it may take a while to enter all the variables

http://scienceworld.wolfram.com/physics/Geoid.html