Of the two types that you mention, I think on balance I would go for induction. Induction has some excellent features, particulalry around safety/minimal use of energy, but the problems that can occur when attempting to pre-heat pans, i.e. cutting out when the pan is empty, keep me firmly in favour of gas. If you are a wok user, or like to pre-heat iron pans, you could incorprate a stand-alone or portable single plate, or even a gas wok burner, which would be my choice.
If you have a Neff Circotherm that is giving good service, personally I would think twice about changing it.
Modern domestic appliances usually offer more in terms of technical features, but often with less build quality than the older versions.
If keeping your existing oven could be an option, have you thought of buying a good quality combi? I have a Panasonic combi that (subject to the user's efforts) produces excellent results, and I would pit it against a Circotherm any day - the accuracy when baking in convection mode is incredible, and it has fully programmable functions, including a rapid pre-heat phase that signals when the required temperature is reached, plus turntable, auto-off, etc.
As for new ovens, I think AEG is good, but if you have been happy with Neff, then perhaps their latest "upgrade" is the way to go.
