Portable battery bank. 1s or 2s?

I am prototyping a portable charger/ battery pack with anywhere between 6 and 10 cells and am curious as to: do I wire them all in parallel and use a 1s 10A BMS or a 2s BMS ? It is to preform like any other portable charger (for charging phones,etc.) but seeing that portable chargers (store bought) supply 5v, that's where my question arises; 1s with a step up boost converter (to 5v) or 2s with or without step down converter (to 5v)?? Please help.thank you