The regular Ultra comes with a lanyard and pocket clip, which are useful, and also comes in nice packaging, which looks a bit better as a gift. The Ultra-G has hard anodize which is more durable, but you just get the light in a plastic bag, no lanyard, no clip, no nice package.
The X1 has a very narrow beam which most people don't like that much. Other than that it's a very well made light.