Here are the main points to watch if you want to make a successful soufflé: :
The roux must not be allowed to brown (don't overcook it)
The mixture must not be too hot when you add the egg yolks (or they will cook)
The whites must be beaten until they are quite stiff
The dish should be buttered well, then dusted with flour
The dish should have sloping sides (to allow the soufflé to swell and rise during cooking)
For a professional touch you can give the soufflé a flat, smooth top by smoothing the surface with a palette-knife before baking and begin the cooking with 3 minutes under the grill.
As for the cheese, I prefer Comté, but you can use whatever you choose, even a mixture.