Mulled booze for party - what are your tips?

[WifeofDarth]

I love a 'vin chaud' when I'm on a mountain and want to do something similar for a family party, but am slightly nervous about making my own as it can taste bitter.
Do you make a good mulled drink? If so please share your tips!
Wine or cider?
Add OJ or not?
Also I liked the idea of doing it in the slow cooker, that way even if no one drinks it, you get the festive fragrance. But my slow cooker is quite powerful so will it just go bitter/lose the booze?

I do cider in the slow cooker, decent still scrumpy cider i don't water it down at all just add the spices and 2 tablespoons brown sugar.
I put it on high until it is hot then simmer it until its finished.

Lidl's own Gluehwein isn't bad...