I think you make website for people so it must be useful for them so I think domains should be not long, more shotter more better.
Easy to remember, Easy to type, and Pronounceable are characteristic of a good domain name imo. But domains have many variations. 1. Short Domains based on acronyms (ex: UPS.COM = United Parcel Service] 2. Keyword Rich Domains. (Usually targeting search terms / patters for a given product / service) 3. Catcy / Brandable (Usually Made words ex: shopfy) 4. Catagory Killers [ Ex: Diapers.com. This is the master of all the universal Diaper related Domains. Assume .com is the king.] and the list continues with numerical domains etc etc