A few months ago I would have wholeheartedly recommended Ubuntu. However the picture has changed somewhat with the roll out of Ubuntu 11.04 (a.k.a. Natty Narwhal).
To make a long story short, Mark Shuttleworth, the owner of Canonical, the company behind Ubuntu, probably worried by the long term consequences of the introduction of Android, has engaged into a desktop GUI revolution tailor made for the new netbook/tablet market. The result is Unity which many people believe is still buggy and difficult to use. The fact is that Unity is very much "inspired" by Apple's iPhone UI paradigm and does not scale up very well if you are used to normal or to large size screens. If you wish to judge by yourself which problems are encountered by newly migrated users, take a look at the Ubuntu stackexchange community and search for Unity or 11.04. The worrying thing is that Canonical is still deaf to the critical feedback and will impose Unity as the only GUI in the upcoming 11.10 - a disturbing prospect for long time fans such as myself.
So, if you are ready for new tablets/smartphones GUI experiences and are prepared to look into crash/hang and compatibility problems I guess you can still go for Ubuntu.
On the other hand mint has a more reasonable approach and is supported by a steadily growing community of enthusiasts. Above all its leaders don't believe they own their users, so that new software is not pushed on your disk in the way Ubuntu folks do.