I am using iPhone 6 now. Which one should I buy next?
Apple customer service told me that iPhone 6 can do everything iPhone 9 or 10 does except picture pixel.

Yes it can do everything and don't need to upgrade if you ain't using other than to browse, text and make calls. Unless you want phone with better picture capabilities such iphone 8 which in good deals.

if you don't need a new one, don't buy a new one.

If you are tempted to get a new one and cannot help it, get the next model that has significant differences. maybe iphone 8?

आबसकता , चाहना , बगली र भिडभाड संग मिल्दो जुल्दो मिलाएर एउटा किनी देउ | ब्रो ले पडेनौ : अमेरिकामा आएर अमेरिकी जीबन बिताउन नसकेका नेपालीमा किन दर्ता गर्नु हुन्छ ?
दाइ हरुले लागेको पैसा दिए गाडी फेर्नु पर्यो बनि दिदि संग गुनासो गरेको त , किन न Installment किन दुखेसो गाइ बस्छोउ भन्नु भएको थियो | किस्ता बन्दि मा तिर्ने हो हान्देऊ हान्देऊ | साझामा नसोधी हान्नु पर्ने |

What happen to your plan? Did you buy or not?
What will be your next shopping ?

6s is pretty fast. if you like Bigger screen, 6s plus. Save money man.