Depends on the size and how you want them to look. My FA Cup banner was just black tape stuck directly onto yellow foil, took about 30-40 minutes but it isn't the prettiest and only works for quick message banners that are a certain size.
For larger, prettier displays you need to cut out letters using a blue foil and tape them onto the yellow foil. Probably the simplest, least messy way of making large banners and surfers.
Painted banners look the coolest, and have that rustic European Ultra look. Unfortunately they take ages to paint, easy to ruin halfway through, and you have to leave them out somewhere to dry which isn't easy when they're big. I can't believe we painted so many!