If you live in an area with some seriously steep areas (like San Francisco) or you are in bumper-to-bumper traffic regularly for lengthy trips (like really long commutes to work), an automatic may be the easier choice, otherwise your left and right legs will get tired.
If you care about your car and want to get the most out of it, get a manual transmission. In cars where both a manual and automatic transmission are available, the manual versions tend to accelerate more quickly (probably due to better launch control and gearing) and get better gas mileage (also due to gearing, since they tend to have another gear over the automatic, except in a few new cars). In addition, you just have more control over the car, as opposed to having an automatic where even when you have some sort of "manual"-like control, it still isn't the same. For example, even if you press the button to make an automatic downshift, it has to go through the car's computers to make sure that it is safe, and if it is safe it will then downshift, whereas with a manual, it just shifts since you're in total control. Manual will only mess up if you don't know what you're doing (i.e., shifting into too low of a gear, grinding your clutch, etc.). Manual rocks.