Which is the biggest festival for the Jews?

No quite sure on the meraning of the word 'biggest' here. I've listed the most important but chosen to take 'biggest' as in like longest which is Hanukkah. Its also not as solemn as the other festivals so I thought that might make it 'bigger' in a different way

The most important Jewish holy days are the Sabbath, the three pilgrimage festivals (Passover, Shavuot, and Sukkot) and the two High Holy Days (Rosh Hashanah and Yom Kippur). It is forbidden to work on any of these days.

http://www.religionfacts.com/judaism/holidays.htm

Hanukkah also known as the Festival of Lights, is an eight-day Jewish holiday commemorating the rededication of the Holy Temple in Jerusalem at the time of the Maccabean Revolt of the 2nd century BCE. Hanukkah is observed for eight nights, starting on the 25th day of Kislev according to the Hebrew calendar, and may occur from late November to late December on the Gregorian calendar.

https://en.wikipedia.org/wiki/Hanukkah

"Yom Kippur, also known in English as the Day of Atonement, is the most solemn and important of the Jewish holidays."

https://en.wikipedia.org/wiki/Yom_Kippur

"Yom Kippur is probably the most important holiday of the Jewish year. Many Jews who do not observe any other Jewish custom will refrain from work, fast and/or attend synagogue services on this day."

http://www.jewishvirtuallibrary.org/jsource/Judaism/holiday4.html

The Torah considers the most important festival to be Passover, and sets the Jewish calendar with the month in which Passover occurs as the first month of the year (Exodus 12:2). Passover is the first festival mentioned in any list of the feasts of the Jewish year, after the Sabbath. In Israel, Passover lasts for seven days, with the days before and after gaining cutomary importance of their own. In the Diaspora (outside of Israel), Passover becomes an 8-day celebration.