About portable charger iphone 5, to buy 2600mAH or 5200?

Also the ones on ebay under $10 are good? How do you use it? What's the best portable charger under $15 on ebay?!

The higher the amperage rating of the charger the faster it should charge your battery in theory… So the 5200mAh charger should theoretically charge faster than the 2600mAh charger