DS3231 Vs DS1307
The main difference between the DS3231 and DS1370 is the accuracy of time-keeping.
DS1307 comes with an external 32kHz crystal for time-keeping whose oscillation frequency is easily affected by external temperature. This usually results with the clock being off by around five or so minutes per month.
However, the DS3231 is much more accurate, as it comes with an internal Temperature Compensated Crystal Oscillator(TCXO) which isn’t affected by temperature, making it accurate down to a few minutes per year at the most.
DS1307 is still a great value RTC and serves you well, but for projects that require more accurate time-keeping, DS3231 is recommended.