I've never tried adgreek, but I've always had great experiences with
greeknation.
The majority of their items are for national organizations, but they do have several items that can be custom made (ex. instead of asking "Do you want to order a red Omega Delta Phi jacket?" they'll sometimes ask you to give your greek letters and color combinations for the orders). I've ordered single items every time I've shopped there, and it's never been an issue.