Hi, I'm not too sure if this is the right place for this... but it seemed most appropriate.

I have an audition for a talent show at the end of january -

I am going to sing 'feel' by robbie williams, and also play something on my guitar.
At first, I leart 'last horizon' by brian may, but thought sounds really simple.

What would piece could I impress them with, that portrays my playing and technique... without 'giving too much away'?
I like Queen, Muse, Jimi Hendrix, GNR... classic rock mainly

The judges don't know anything about guitars btw

Of the artists you mention, I don't know much about Muse but the only one I know has solo pieces is Hendrix - most of his songs can be done with just an electric guitar and voice. I guess GNR has a couple of acoustic ballads that might work.
GMW hot-rod telecaster
GMW soloist
PRS Custom 24
The Illegal Les Paul
Soldano SM-100R
Splawn 4x12

“Life is on the wire…the rest is just waiting” - Papa Wallenda
Substitute the stage for the wire, and he's got it.
Depends on your skill level... if you can play well enough, then guys like Michael Angelo Batio and Stevie Ray Vaughan who will show off a ton of skill while still being extraordinarily melodic would work well. Sure, it'll show off most of what you can do to begin with, but there's a huge bank of stuff there so it's not like you'll run out of material.

If not... then maybe compose something of your own that's based on sounding good rather than showing off immense tech skill?
Hendrix is never a poor choice. Take something of his that's recognizable and either play his solo(s) (which are always a fair choice) or if you're up to it, write your own solo to show off your skills.

Just remember, if the judges don't know a thing about guitar, playing even a simple pentatonic run will probably impress them. A lot of classic rock guitarists aren't particularly technical. They are, however, excellent showmen. If you play a bit of Bohemian Rhapsody or Purple Haze and seem to be into it, you'll get a better response than if you were to play Altitudes and just sit there looking bored.
Is there any instrumental I can play? Because i'm already singing a song separately...