Francesco,
I've been quite happy with SmugMug ( http://www.tomoscott.com ).
Truthfully, I think Smugmug, Zenfolio, and Squarespace all offer comprable features.
One think I've been happy about with SM is that they've built apps for Android, iPhone, and Kindle, which makes it a lot easier to show someone your portfolio when you're on the road. Again,though, I wouldn't be surprised if the other major players have apps as well.
Customizability is a two-edged sword, especially if you want a design responsive to all types of devices. That's why, for example, SmugMug doesn't allow you to add javascript to your pages.