Mandriva One 2010.0 (including Moblin UI)
Mandriva Linux is one of the long-established distributions, and it just keeps getting better. There are plenty of reasons to choose it on its own merits, as it is a good, solid, stable distribution, it has wide support in the Linux community, and they do a good job of keeping up with the latest packages and device drivers. But in addition to all of that, if you have had trouble with the new Ubuntu 9.10 distribution, or you are a bit reluctant about it because of the numerous reports of problems circulating... or even if you are just becoming uneasy about the direction that Canonical is moving, then this could be a very good time to take a look at Mandriva Linux.
I always use the Mandriva One distribution, because I want the added proprietary drivers and packages it includes. If you want to stick with a strictly FOSS distribution, you can choose Mandriva Free. If you want the "Full Monty", with support and printed documentation, go for the Powerpack distribution. There is generally also a "Mandriva-On-A-Stick" USB drive option, but it doesn't seem to be ready for the 2010 distribution quite yet, it should be out soon.