I have the avior. It's great!
It's slightly large tho, I forgot to read the specs but over a few weeks I quickly adjusted to it.
The scroll wheel is firm and solid, the side buttons are easy to press.
The avior has customizable options for everything. Every mouse button can be changed to another function.
LEDs have many options with many patterns if you like that kinda thing.
It's a bit heavy actually, not sure about the grams but I think it's heavier than the zowie (not sure).
It's also ambidextrous, but very comfortable for me (right handler). Slightly expensive and it's good if you can get it for around $60 or $55.
The zowie apparently has horrible side buttons. Like really really hard to press.
Also it has set(nonchangeable) DPI so you cannot change it.
Other than that I hear it's pretty good.
If you love customization and need and want to adjust your DPI, the avior is great.
If you're fine with the zowie set DPIs and don't really use side buttons, then that is great,