Selene's is better between half moon and new moon assuming wiki is remotely close on the estimated racc/ratk moon values.
It's more accurate but slightly less powerful between waxing/waning from half moon and full moon. Having 10-15 more racc at the cost of 5-10ratk isn't a terrible trade off.
The main concern with Selene's is you need to adjust your macro depending on the moon if there's a potential racc overload.
So best case scenario Selene's is down 1str, 5racc, but up 10ratk. "Worst" case it's down 1str, 10ratk, and up 15racc.
Don't forget that Selene's has ranged accuracy and Fay only has weapon skill accuracy, so Selene's affects TP with net 30 stats of racc/ratk whereas Fay is only 15ratk.
Edited, May 4th 2010 12:50pm by Requim
80 Pup Brd, 75 War Rdm Drg Sam Mnk Pld Bst Thf Whm Nin Smn Blm Rng, 72 Drk, 63 Cor, 50 Blu, 40 Dnc Sch