Bottle is very cool, but Flask has far more plug-ins ("extensions") than Bottle does. Flask has nearly all the features that Django does, only they are in the form of dozens of separate extensions. In my opinion, this is a good thing. It's easier to understand the framework when you start with the basics and learn more as you add on extensions.
I believe that Flask will move to Python 3 eventually, but at the moment I agree with the decision of Flask's creator (Armin Ronacher) to stick with Python 2.7. In the end, Python 2.7 is probably better for someone new to the language. There's more documentation, and it's still the default Python on most systems(although a few are starting to pre-bundle Python 3).
I believe that Flask will move to Python 3 eventually, but at the moment I agree with the decision of Flask's creator (Armin Ronacher) to stick with Python 2.7. In the end, Python 2.7 is probably better for someone new to the language. There's more documentation, and it's still the default Python on most systems(although a few are starting to pre-bundle Python 3).