I've heard 6 of these. My favorites, Logitech UE Mini Boom (BestBuy @ $70 now) and a Enerplex 1 1/2 inch generic cube speaker ($5 from Frys on sale). I've also heard from friends and family, the JBL Flip, Dell and several other generic brands.
My ears are picky and I play acoustic guitar and I'm mostly blown away by the $5
Enerplex. The speaker they use actually looks a lot like the same ones Yamaha uses in their surroundbar back in the early 2000's. I've also seen the Enerplex on sale as a Nakamichi at KMart/Sears. Smooth mid-range, plenty of bass too out of 1 inch speaker and plenty of amp power, with minimum distortion Surprizingly long battery life. Wireless range is only about 10 feet average. When nothing is playing there is this constant background squech, but it disappears as soon as something is playing.
The Logitech UE mini boom, my future better-half loves. It's sound can easily fill a room and she doesn't mind that it's in mono. You can buy two to use in stereo. Great sound like the Enerplex and much more polished, but also more expensive.
I recommend getting both. I use the Enerplex for podcasts and the other half LOVES the UE Boom for music, even if it is in mono. A good roundup of Bluetooth speakers is from
wirecutters.