[Q] Battery Packs topic

Hi, I just bought an 18000mah battery pack from amazon by EC Technology, it has 2 outputs, one 1AMP and another 2.1Amp. My Nexus 5 charges at 1.2 amps, would it be safe to use the cable that came with the phone in the 2.1AMP output or am I better off using the 1AMP. THANKS ;)