I voted Tough Call in the poll and why I made this thread. Because an example would be ok if it's just a 1% difference, then I can pick the more fun ability. But if something is slightly less fun, with slightly less dps but I like their cosmetics more... then I would pick that.
Not sure I really like the set up of having to tie mechanics to cosmetic choices. With regular gear you use the ones you want for stats, but can transmog to what you want.
The individual pieces of the covenants I like, but I think everything people predicted would be a problem or annoying ... is.