I am considering buying an android phone, and two possibilities (at equal price) are the Samsung Galaxy S and the Google Nexus S (made by Samsung).

Some thoughts:

• The Galaxy lacks a flash for the camera.
• The Nexus doesn't have removable memory.
• The Nexus doesn't have an FM radio.
• The Galaxy comes with horrible Samsung addons, while the Nexus is cleaner, and is more likely to get updates.
• It might be hard to update the Galaxy anyway, as the update tool from Samsung requires windows, though it looks like there might be some alternatives that support linux.
• The nexus is ~10g heavier.