I have used Vistaprint from the beginning for the invites and still now for Christmas cards. Their quality is excellent and service. You don't like the quality of the photo, you can chat with them, and they will print a new set for free and ship it to you.
Definitely recommend Vista Print or Zazzle! We’ve ordered from both multiple times and have always had great experiences with both quality and speed of service! Shutterfly is wonderful also, however you’ll have to factor in that they are priced in USD.