Primarily, manufacturer and underlying technology. A federation holodeck uses replicator technology to create shapes and textures, and then "paints" them with photons. A cardassian/ferengi holosuite uses transporter technology to achieve the same effect.
it is based on size, holodecks are much bigger than suites.
Kitface 19:34, June 29, 2011 (UTC): Yeah, replicators use transporter technology - so the distinction is vague. A holosuite is simply more personal than a holodeck. Smaller size. This picture http://ent.trekcore.com/gallery/albums/4x22/thesearethevoyages124.jpg shows that it's labelled "holographic environment simulator", so the terms "holodeck" and "holosuite" are likely just shortened terms that people came up with that conveniently distinguish between the different sizes of HESes.