This appears to be a very common question, that in its broad sense is really about digital vs hard copy or old school vs new school (not inferring age here). In my experience, I would send a hard copy, though sending both is not bad either. Touch point is key here. In addition, with a hard copy you have absolute quality control. i.e. how the colors and text read. You will not have that control digitally with monitors all be calibrated differently. Ask yourself this, if you were invited to a friend’s wedding, would you rather have an actual invitation that you received in the mail, or an email/evite invitation?