A Bluetooth speaker that sounds really great?

Ultimate Ears ( UE Boom) are good and can be paired.

I have a pair of Ultimate Ears Megaboom 3s. They can be paired in stereo, are waterproof and omnidirectional.  They were my go to speakers when I had a Hot Tub. Great sound, bass and long battery life. 

I have a pair of Sonos Move 2 that I use in stereo.  They sound pretty good for speakers that are portable and weather resistant.  I’ve listened to the Harmon Kardon Play 3 and it’s the best sounding portable single unit I’ve heard. 

Sonos Move2! Sounds exceptional for Bluetooth. Sonically adapts to its surroundings. I which it was compatible with BluOS so I can use it when I barbecue with Bluesound systems. Think I’m going to get a Bluesound pulse flex and battery pack just for that reason but as a stand alone it’s pretty darn good!

Couple years ago when Amazon had there yearly big sale, I bought a Bang & Olufsen Beolit 20. It's rather pricey, but sound quite nice.

I generally avoid apps, but the  Bang & Olufsen app allows custom tone adjustment.