Originally Posted by james_ant
The G400/MX518 and below have always been made out of crappy materials. I never had any problems with two G5's I've had. One of the G5's has a malfunctioning sensor a week or so after I got it, but a simple call to Logitech and they mailed me a new one no questions asked. There really shouldn't be a problem with Logitech mice above the G500.
I disagree, having owned an MX510, 518, G500 and G700 and having known three or four others with the 518 only one of them had a problem with their mouse and it happened after five years of gaming.
The 518 is well built, it doesn't feel as expensive as a G500 or G700 but it's reliable.
Mine is almost four years old and works perfectly.
Out of the four options above I play with my 518 because the G500 and G700 have very noticeable acceleration.
It's probably also worth saying that the same person that broke the 518 had a G5 that lasted about a week, he also has another G5 that I think is broken.
I'm not implying the G5 is a bad mouse, just saying the 518 is about as reliable as they come.
OP, I've only used the 518 out of your two choices and I'm very happy with it but don't know enough about the Zowie to compare them.