I agree totally with the points made by Ged Fox & Big Al.

I tend to try & sing the opposite of what my predecessor has sung. That usually entails having a 'light' and 'heavy' song at the ready.
I once saw a folk band toiling with dreary ballads in a bar full of drunken rugby supporters. I was asked to sing and did a rendition of some spirited drinking song which oddly got their immediate attention.

It should be generally horses for courses - or you could just do your own thing and stuff the rest of mankind.