I'm going to buy a good portable speaker but I don't have enough ideas which one to choose.
The best for me is Marshall Kilburn II, Harman/Kardon Go Play, JBL Boombox. I often leave the city and for me is really important the quality and max. volume of the speaker. I have been listening both Harman/Kardon and JBL Boombox, but not the Kilburn 2.
Secondly, I would like to hear mid frequencies and bass.
Can you please recommend what to choose.
Any of those are good along with UE Boom models. Asking someone to pick speakers for you among several good models is like asking others what you should get for dinner. Grab one of the better ones and you should be fine.