Totally agree: play a song in whatever key works best. It's not always what's best for the singer, either.
Case in point:
When THEE DIRTYBEATS covered The 13th Floor Elevators' "Fire Engine", we did it "B".
Now, the original version, in "E", is very cool; but we really admired the intro Television added (see their 1978 live album "Blow Up"), with that insane chromatic chordal build. And Television's version was in "Bb".
As we worked up the song in Bb, we found a terrifically vicious downslash effect could be achieved on the I-IV transition if the IV chord was actually an open E rather than a barred F. So we transposed the song again, this time *up* a half-step, from Bb -> B.
You can hear that guitar downslash at 0:54 (it's wonderfully noisy, if you're into that sort of thing) at http://theedirtybeats.bandcamp.com/track/fire-engine. Changing the IV to E also freed Jamie to add a soaring thing to his fuzz solo. While the higher key forced me out of my comfort zone as singer, it kept me on edge and reaching, which for a highly charged rock performance isn't necessarily a bad thing.
We similarly fooled with "Shape Of Things To Come", originally recorded in F# by Max Frost & The Troopers. We did it in E, because my guitar solo just fell out that way.
-A
THEE DIRTYBEATS maximum vintage garage
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