Hi,
I assume the "searchable webpage" refers to [https://pokemongo.gamepress.gg/comprehensive-dps-tdo-ranking] while the "google spreadsheet" refers to one of the three external spreadsheets linked in this page [https://pokemongo.gamepress.gg/tdo-how-calculate-pokemons-ability].
The two pages are maintained by different people, and there are minor difference in their respective assumptions, mathematical models, and parameters, hence the discrepancy.
As for which is more accurate, the lazy answer is: whichever produces closer results to simulator's is more accurate. We haven't conducted any full-spectrum test for either page, nor do we plan to; We are putting our focus on improving just one of the models continuously.