There is no way to answer your question without more info. Stem's vary widely in length, rise, and size of handlebar they accomodate. The stem you should get should be driven by how the bike fits you -- combination of rise and length puts handlebars in position that you can comfortably reach while riding. Whether you want bars higher up, farther away, or closer to you, will determine stem you get.

To answer question about length, a 60mm stem will put handlebars 40mm closer to the rider than a 100mm stem. Stem length is generally measured from midline of the steerer clamp to midline of the handlebar clamp. As for the "mean slanted look", you may not want that if using a stem with very little or no rise puts handlebars so low as to make you really uncomfortable on the bike. Here is an article about stems. http://www.brightspoke.com/c/understanding/stems.html