They have a great selection, I mocked up a few invites for my annual Christmas party and it was a seamless experience. They have a great selection, both printed and electronic. They also have partnered with many famous designers including: Kate Spade, Jonathan Adler, Sugar Paper and Oscar de la Renta to name just a few.
The great thing about sending an electronic invite is you can easily obtain an RSVP - which is hard with a paper invite, and frustrating when people do not RSVP in a timely manner. Here they can easily click yes or no! I find this to be a great feature.
I would highly recommend using Paperless Post, especially with all its great designs!