So far I've been to Riften, Whitetun, Solitude, Windhelm, Winterhold and Morthal.

So far, I'd describe Whiterun, Solitude, Windhelm and Riften as... main Holds. Morthal and Winterhold feel really small, and more like villages.

Of the remaining undiscovered Holds, which are more like large towns, and which like small villages?