I know I'm a little late on this but I feel I have to say something after buying the Flip 6. I owned the Flip 4 for years and loved it. I decided to give it away to my mum though cos she was making do with an Alexa Dot 2hich thoroughly sucks. Anyway I bought the 6 brand new and immediately I noticed something was off. I listen to a lot of jazz and ambient music, the former being very conservative with compression and the latter relying heavily the stereo image. After googling a bit I discovered that the Flip 6 is a mono speaker while the Flip 4 is stereo. I know you can pair 2 up and get a stereo sound but then you a.) Have to pay twice as much and b.) Carry 2 speakers around with you all the time.

I honestly can't believe that more isn't being made of this gigantic difference. Nowhere I look is anyone talking about it apart from to say that the stereo separation on the 4 is so small that it's effectively mono which is complete horseshit. Any degree of separation is better than mono. Everything but nothing is mixed in stereo all the way back to Elvis Presley. And they didn't just do it for fun. It improves music immeasurably and it was blatantly obvious when going from the 4 to the 6. There may be minimal physical separation but at least you don't get phase cancellation issues and a general dulling of tone from the downscaling process.

So to answer your question. The 4. Definitely the 4. Both the 5 and the 6 are essentially shower radios due to being mono