Giovanni,
telling you what initial DSLR you should buy is presumptive at best. It depends on what you shoot currently, what you intend to shoot, how you intend to output those images and how much you intend to invest in your system.

The good news is that all the systems currently offered by Canon, Nikon, Olympus, Fuji, Sony, Panasonic, etc. are excellent. You can't go wrong with any of them in terms of being better than what you are currently using.

The key is expandability and how that fits in with your photographic objectives. All of those manufacturers make good bodies and great glass. All make the rest of pieces of a complete system: flash units, macro accessories, etc. So the best thing you can do is go out and actually handle the cameras you are considering. If possible, rent them and use them for a weekend or a week. Once you have a feel for how they handle and how they fit your style, you can decide what to buy. And always remember that the lenses you put on your camera are always at least as and possibly more important than the camera body itself.

That may not answer your question directly but that's because it's impossible for anyone else to answer that question but you. Good luck with your decision.

Jim