I’m hoping to hear from people involved in classical or Musical auditions. In an audition for, say, a choir, they want you to sing an aria is it best to select a piece originally written in a key that’s good for you or is it okay to transpose a piece you like better to suit your voice? What about if you’re auditioning for a school to get into their program?
Lastly, do opera or musical directors ever transpose pieces to fit the artist? When I played flute for Miss Saigon, it seemed like we had another key for the understudy.
I do audition for choirs, don’t really plan on doing any solo auditions but I’m curious. I’m a contralto and there are just more interesting pieces for mezzo soprano, it seems. If you know of any good alto arias or “showcasy” pieces I’d love to hear about them.
Former musical/opera singer here. 
If you’re auditioning for a choir, a transposed song would be fine. They want to hear your vocal ability, range, tone and sense of pitch; it’s not as if the music or choral director needs to know whether you can sing a specific aria in the composer’s original key. Of course, you definitely want to find a piece that best showcases your voice, irrespective of what part it was written for.
(OTOH, if you were auditioning for a specific role – I dunno, let’s say Dalila in Samson et Dalila – then you’d need to sing “Mon coeur s’ouvre a ta voix” in the correct key.)
I think it’s pretty rare for professional productions to change the key of a song in a musical to suit a certain performer, unless that performer is a star whose needs must be accomodated. In opera or classical music, it’s even rarer – perhaps an aging or ailing superstar like Pavoratti on a last tour of Aida might get accomodated. The music critics and operaphiles would probably lambaste anyone else for ‘cheating’.
Musicals in workshop phase may get tweaked by the composer if s/he finds the performers are having issues. But considering musical theater is glutted with talent, it’s often easier to replace the performer than expect the composer to change the orchestration. (Again, unless the performer is remarkable for some reason – supremely talented or a big box office draw.)
Anyway, what aria were you thinking about singing? Sometimes a good audition piece will depend on the type of choir you’re planning on auditioning for. For smaller chamber groups, you might want something less flashy or bravura; usually they want good blending voices. Large groups may want bigger, gutsier voices (though they still want blending as well).
Whew, sorry for the long answer. Hope this helps!
Great answer, thanks. I didn’t really have anything particular in mind. I’ve been working on “Parto, Parto…” and it sounds so much better if I bring it down a major third. There’s a large choir that I’m thinking about, probably not for a few years. I imagine I’d probably use O Thou that tellest good tiding to Zion from Messiah, maybe. It’d be cool to get into an opera choir tho’!