Best? There is no such thing. There are too many variables for any absolutes. I'm surprised that nobody has mentioned the Quad ESL 57. There was a recommended 25 wpc maximum on those if I remember correctly. Sure some will like horns, personal preference and all that.
After having many different types and styles I settled on VPMS Tower II many years ago and have never looked back. I picked up a second pair and can drive both pair with a 20 wpc tube amp with glorious results.
Best? There is no best. It's all in what you like.