I first started with the US december issue, and was very pleased with the readability, extras provided by the iPad version (animations, links to videos or URLs in the text, ...), horizontal viewing format, and content.
I then bought the UK version...and soon realised that it was in no way comparable to the US version: I cannot read it with the iPad tilted horizontally (or is it just me ? I tried to reboot, looked back at the US version to make sure it was possible, ...), there are very few "extras" and when there are...it feels like they do not belong there and have been added just because they were expected by the reader..
The content in itslef is fine, even if I found an article which I had already read in the US december issue.
I'm not too sure I'll be buying it again next month...I might stick to the US edition...