Rotosound R9

The strings sound and play great, much like any nickel plated steel strings. But where Rotosound differs from other manufacturers is the quality in how they create the ball end wraps/fastening. When you compare these with other (big name) brands you will find a much securer and longer wrap around the ball end. There's very little "slack" around the ball making tuning stability much, much better than most other brands. The length of the wrap is also much more consistent (compare with any other big name string manufacturer and you will often find good AND really bad wraps around the ball end).
The color coding of the ball ends are also much smarter than how others do it (3 colors instead of 6).
The packaging is also excellent with just one hermetically sealed package and not seven different ones - an outer package and then one each for the six strings, like many still do it.
And like many here have said, the extra high e-string is a great bonus, although I find that it's seldom needed since the strings don't break unless you have some burrs on the bridge saddles or similar.