We have had many days on the NEW Sinister X5 last season teasing, and have used the Aviators for a couple years now. Here is the nitty gritty from our side of things. Plusses and Minus of both....
SINISTER X5
PRO
~Incredible visibility with the new vanishing frame and larger lens (Nearly the same as an aviator)
~Traditional frame size and shape fits most helmets
~comes with nose protection and three layer foam that really seals to the face nicely
~outrigger design keeps the foam planted to your face without pulling to hard
~tons of lens options, and they are AFFORDABLE to try a couple
~24 designs and colors for 2014
CON
~Not yet truly compatible with quick straps without modifications
~have had complaints about the chrome lenses being extra sensitive to scrapes and give off a reflection on the inside
AVIATOR
PRO
~HUGE area of visibility, nearly 18* more than most goggles
~Frameless technology keeps any snow dust from sticking to frame edge
~trendy design, and fits the new age rider
~fills up large size helmet gaps well
~tons of lens options and colors, and once again affordable
~can change the lenses in under a minute if you practice
~three layer foam keeps even the slightest snow dust out, but is kind to the face
CON
~does not fit well with smaller helmets because it is larger
~not truly quick strap compatible
As for the lens question there is not a true good answer and never will be in the industry. Peoples eyes are all different after all. For our office staff, we all carry a clear tinted lens in either rose, orange, yellow or blue, and then we each carry a polarized smoke for the blue days. It is inevitable that you will need two lenses at least or two goggle setups to truly be happy with most conditions.
Hope that helps, feel free to shoot us any questions or comments.