For the past few months, I was carrying the T-Mobile version of the Galaxy S II, the Samsung phone featured in this awesome commercial that I can't stop watching and laughing at.
A few days ago, my friends at Google sent me the new Galaxy Nexus. So I switched, which is super easy if you use Google's cloud services. Just pop the sim card in the new phone, login with your Google credentials and all the magic happens over the air.
The two phones are very similar. They both have huge beautful screens. Reading on them feels like reading on small tablet. I prefer the menu buttons at the bottom of the Galaxy S II, but that could just be a matter of getting used to the different ones on the Galaxy Nexus.
I prefer the Nexus series because they come with a clean build of Android on them without any carrier add-ons. But I was able to reconfigure my Galaxy S II without too much work.
I would highly recommend either of these samdroid phones. They are both awesome. The ad says it all in my mind.