Best Experience for Aspiring Entrepreneurs?

Sales (WSJ). There's a bit of a sleazy used car sales approach / 'selling freezers to eskimos' stigma with sales. The irony is it's probably the least effective form of sales. Not many of my classmates from university started out in sales (and substantially fewer started or ultimately chose the entrepreneurial route - in fact I can probably count the number on 2-3 fingers) and that's unfortunate.

Sales at its core is the end mile of solving someone else's problems. The rejection/instability is also useful for figuring out if you have (or building) the EQ to deal with being an entrepreneur.