I recently got the straight Vortex Viper HD 15-45x65 as my first spotting scope, and I'm very happy with it. It's the first high-end spotting scope I've handled, so I don't have a point of comparison to Leica/Swarovski/Zeiss products, but I can't imagine why I would need a better picture than this. In addition to the clear picture, everything about it seems rock-solid, and every moving part is really smooth.
My only little nitpick is that the neoprene protective cover it comes with doesn't have a very good hole for the focusing knobs -- the sides of the hole are always coming into contact with them and making focusing annoying IF you're using it with the cover on. This could be fixed with scissors by someone who cared, but I wasn't planning to use it with the neoprene cover on anyway so it doesn't matter.
Pros: Optical clarity, build quality
Cons: None
This review was written in the old system and had content requirements that are different than reviews written today.