Slide film tends to have better color representative, to my knowledge. Slide film is often more expensive than print film, but processing is cheaper (since there are no prints to make), so the entire cost can be less. But then a lot of places don't process E-6 anymore, so it could be harder to find some place to do it. It's a little harder and more expensive to get a print made from a slide, than from a negative, and due to the process, the colors you get may not look the same as your slide did (at least that's what I've found when I tried getting prints made from slides, they never looked right...)