Whatever key gets the best vocal performance from the given vocalist. For myself that varies greatly from song to song. But, most of the country songs I cover I happen to do them in the original key done by the person who made the song popular. That is likely due to me choosing songs that I sing well and learning them mostly by ear. A few I will lower or raise a half step.
For worship songs I try best to choose keys that I think the majority of people can sing them in even if it's not my best key. I have heard very nice worship songs done in bad keys where the lead singer sounded okay but the rest of the people where very uncomfortable joining in. Then I've done those same songs and heard others do them in appropriate keys where everyone feels comfortable and sings along.
So, for me it's largely dependent on the vocals.
For guitar instrumentals it really doesn't matter but I prefer to avoid Eb and Bb.

Does the noise in your head bother me ?