If you get a table with a lift mechanism you can have it recessed or level, depending on what you're doing at the time. The lift can be purchased separately if you're building your own table. Here's an example -
http://www.rockler.com/sewing-machine-lift-mechanism
I much prefer having my machine recessed in the cabinet. It is a little harder changing the bobbin, but I'd rather have that problem than have the machine at a different level.