It depends on budget/time etc
I've used pre-printed badges where we've set an excel sheet to the printers and had spares printed. Spare can be fed through the printer or hand wrote - also messy
I've used perforated sheets for printing in-house. Mail merge and printed in advance with spare for print on the day - messy
I've used pre-printed badge which is sent integrated into the delegate letter. Spares are printed on the day using the same format - again messy
I've used the single badge printers, but this can be costly
This year I'm inclined to use electronic check-in, but we'll still need name badges:S
I was visiting a venue yesterday where there was a LUSH corp conference. They used a 'slate' type of badge with each customized by the individual with their name and what they were looking for, i.e., advice, collaboration, etc. - nice idea although my handwriting is illegible!