I use Luigi's built in grip case as it accomplishes several things that I am after. Most importantly, the leather gives me a sure, non-slip hold on the camera even when it is very hot and humid and my hands might be slick. The built in grip is very ergonomic, and while hard, it is not as hard as plastic or metal, so it is forgiving on your hands for a whole day's shooting, particularly with heavy lenses. The other advantages are that it protects the bottom and rear of the camera from bumps, scratches and minor shocks, while making the camera a tiny bit quieter. On the downside, it adds approximately 15 seconds to the film changing process and if it is not black, it can make the camera less discreet.
For a strap, I use Luigi's hybrid strap. I like using a neck strap, though I rarely use it around my neck. Since the strap is thin, it is easy to wrap around my wrist and carry the camera at my side. This may be hard to visualize, but it is a very effective method: First I put the strap's neckpad on the top of my wrist. Then I wrap it clockwise over the right part of the strap, and then slide the wrist under the right side of the strap, and then over the left, wrapping counter-clockwise. This gives me a very secure hold on the camera, and even if I let go of the camera completely, it will not fall. It also allows me to carry the camera at my side support the weight of the camera with my arm, not my grip. When shooting for a whole day this makes a big difference. Why not a wrist strap? Well when I want to change film I can just put the camera around my neck. Same goes for changing lenses or whenever I want a free hand. That is the advantage of the thin camera straps...they can be either a wrist strap or a neck strap depending on the situation.