I just got back from a long trip abroad in China, and the Satechi iCel Battery Pack is the only pack you should consider that combines it all:

1. Portability

2. Power capacity vs Size

3. Durability

4. Power Output (2 Amps, charges iPads and any USB device you throw at it fast!)

5. Style

6. Durability - Just throw it in the bag, no worries about connectors going bad, or scratches (high quality plastic).

Sure, its more expensive than the competitors for a similar advertised (but untested by me) battery pack but the additional price increase is well worth it!

I will post more about other packs that I also travelled with and tested for my mobile hotspot, and electronic power needs.