Which POS i have to use which one is the best?
In addition to the default POS available in ERPNext, there are other community extensions that expand the range of functions or have a different graphical design. You have to see for yourself what you need or what you like. 
Personally I think the ERPNext POS is already very good, but it always depends on your specific requirements.
Maybe you Like POSNext
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There are 3 in this list - GitHub - gavindsouza/awesome-frappe: A curated list of awesome things related to the Frappe Framework
and 4 on this one - Frappe Cloud Marketplace
probably more out there