For custom, id recommend flat awesome plus. Super fast, easily customisable, extremely stable, and doesnt break with every upgrade. Read reviews about steve and russ on this site and compare what is said about the other competitors products. Oh and they provide actual support.
Probably UI.X and Flat Awesome by the two main theme creators, Themehouse and PixelExit respectively. Both themes come with their own frameworks which are highly customizable and easy to use. Regardless what anyone else says, both themes and their designers are great and have created products that will enhance any site.