Going to a baseball game..need help in determining best seats?

I wanted to get some tickets to see the Diamondbacks vs Rockies Wed in Arizona. I am not wanting to spend a lot of money, and wanted to know....is it better to sit near the bullpen (closer to field, but what are the cons) or the bleachers (closer to field but far away from home plate) or in a higher section (probably the top behind home plate) or infield or outfield. I don't know much about baseball, but I am interested in being able to see something. Thanks