Which is bigger, 11 count or 14 count cross stitch?

The main difference between any count fabric is the number of squares per inch fabric.

The higher the count, the smaller the holes as well as the size of the finished project. 

If you have a frame you wish to insert the finished product, then using the appropriate stitch count will achieve the size you need for a frame. 

You may have a project that is solid coverage, then using 14 Ct Aida is a great choice as it is easy to see the holes as you stitch away.

When using 11 Ct, you should use more strands of fibers. The recommended is four strands while 14 Ct utilizes two strands of fibers just fine.