One thing users seem to forget is that of choice and expectations. We have a choice in what we use for SL and what works best for our specific needs. Some viewers are better for photography and machinima, and some work best for builders and content creators. This is why we choose certain brands of cars, soap, or computers over others. We are not going to find one that does it all.
We all want to know that the viewer we are using is not being used by certain people for malicious purposes. I also think that we would do well to remember that these viewers are provided to us for FREE and are always undergoing changes by the generosity of dedicated developers.
There are also lots of variables involved with computers (age, video cards, monitors, processors, etc...) Throughout all this, I think it's important to keep in mind that with any viewer -- "Your mileage may vary"