Most denominations of Christianity worship on Sunday, but there are other religions that worship on Saturdays. It all comes down to what day has been deemed the Sabbath, as that is often the day of worship for any Christian or Jewish denomination. It’s not common for Christians to worship on Saturdays.
.If we want to talk about which day the bible says is better, there is only the description of the Sabbath being the seventh day of the week. Most European and Latin countries start their calendars with Monday, which would mean Sunday is the end of the week and therefore the seventh day of the week.
However, the United States starts their week on Sunday when going by the calendar, but most consider Monday the start of the week since that is the first work day of the week.