Difficult to pinpoint just one. I'd have to do it like this:
Studio: In My Defence; Exercises In Free Love; The Golden Boy; Guide Me Home/How Can I Go On (note: mostly solo AND from Barcelona lol)
Live: Save Me (especially Montreal '81*), Who Wants To Live Forever and (very) early renditions of Under Pressure.
Just my opinion :)
* this is my very favourite single performance from Freddie on ANYTHING. Flawless, IMO.
I think it could be:
Studio - Under Pressure
Live - Under Pressure
The "why" part is quite high and he held it for quite long. The studio version has falsetto, normal range and high range.
Prophets Song
Father To Son
White Queen
Flick Of The Wrist
Ride The Wild Wind
We Are The Champions - Live Aid, 1985
Bohemian Rhapsody - Fukuoka 1976 (joking) Live Aid 1985
Brighton Rock
Save Me
Innuendo
It's Late
You Take my Breath Away