I am a fan of many high-efficiency systems, but, most are systems built from high efficiency drivers and custom cabinets and crossovers and not complete packages. I like some vintage drivers and a few modern drivers that are either straight out replicas of old drivers or are modern updates of old drivers; these however, are crazy expensive (e.g., G.I.P, Cogent, Goto).
Of the modern, complete systems, my favorite are the Charney Audio systems utilizing full range drivers in back-loaded horn configurations. Until I heard the Charneys, I did not think that a single driver system could really be a complete speaker capable of playing all sorts of music very well.
For a fairly low-cost high efficiency system (albeit with a built-in amplifier for its bass driver), I like the Rethm Bhaava. At a substantially higher price level, I like the Avantgarde systems that also use powered bass drivers.
For not so high efficiency speakers, I like the entire line of Audio Note speakers, The 093 family of Devores, Trenner and Friedl speakers, Classic Audio field coil driver speakers and Horning.