I like the default Mac US/International English/British layouts (they're almost the same as each other). Mac users are graced by an OS that actually uses the Option (Alt) key on every letter to do something useful. You can type all manner of diacritics and such without using a non-standard layout! It works great for English, German, Swedish, Spanish, French, and perhaps more.

I only wish there was good support for it on Linux and Windows. I will eventually contribute a patch to xkb to fix its version of this.