If you need to charge several device at the same time, I suggest you buy the one which have several outputs. And you must notice the Output current because different device need different current, for example,1A can charge all of the mobile phone but can't charge your ipad, if you need charge ipad, you should choose 1.5A or 2.0A. That is to say, if you need charge ipad and iphone at the same time, you need buy the battery which has two outputs 2.0 and 1.0.
As for the brand, choose the ones who have passed MFI certification will be better, but the price will be much higher, So I think brand is not very important, the most important is the quality and price. Hope it is helpful for you.