Your local high street.
Mail order, internet etc labs can do all they like to ensure next day delivery but **** happens - an envelope can miss the bag, the postie can miss the package, the prints can be simply not good enough for you; in each of those cases, you're up a well known creek without a paddle, while high street prints can be done while you wait (or get a cup of coffee next door) and if they're not good enough you should be able to get near instant reprints done.