The only devices I've found to have decent outdoor use was my Asus Transformer Prime with it's ultra-bright mode, and my iPad Air 2. The former was nice, but boy it got hot in the SoCal sun and the battery life was slashed. The iPad Air 2 is pretty good without _completely_ killing the battery. It's really the nature of the beast with today's media consumption devices that they'll have glossy (i.e., highly reflective) screens that require incredible brightness to overcome.
But, absolutely _nothing_ approaches e-ink for sunlight reading. I have my Kindle Paperwhite and love it, and it's the only thing I regularly use in the sun. Only when I absolutely must do something other than reading to I pull out another device to use.