I grabbed the two new Material themes. The light theme and the previously released "Material" theme seem identical (other than wallpaper and icons that I don't use anyway). I like the "Material Dark" theme, but not fully my cup of tea. I'm sticking with the light theme for now. I wish the light theme had consistent colours (the grey, white and turquoise) in the dialer, not the bright blue. Meh, it's still my favourite.
I also like the "weyo" theme for the black and blue, but I prefer the subtle colours of the Material theme.
I suppose I wouldn't mind paying for a good theme to support the developer, but with the material theme (my favourite and probably what I'll stick with for a long time), being free, I don't have any need to buy others. Also, I'd pay a buck, but $3 is seemingly high for most of the current options.