Where does Hamas rank in the list of terrorist groups with respect to size, organization, threat posed etc compared to others like say Al Queda and ISIS?
We’re talking very different types of organizations, despite having somewhat shared origins. Al Qaeda and ISIS are transnational, global jihadi organizations that regard expressions of nationalism as acts of blasphemy against God. They aim to overthrow regional governments and attack Western and other global targets when possible. They have traditionally appealed to and drawn much of their manpower from a tiny pool of Muslims from across the globe, but have struggled to consolidate a territorial basis - some notable exceptions being the ISIS caliphate of 2013-2016 and the current Al Qaeda run territory in Syria’s Idlib province. They lack mass appeal due to their indiscriminate violence and dogmatic sectarianism, and so their scope for action has tended to remain limited to war-torn peripheries. There are signs that the Al Qaeda aligned franchise groups in certain areas such as Syria have come to understand the alienating impact their actions have on local populations, and have attempted to adjust accordingly, but it remains to be seen if they can expand beyond regions already devastated by war.
Hamas on the other hand are an Islamo-Nationalist movement with a singular focus on the Palestinian cause. They are as much a political party and social movement as they are a “terrorist organization”, a term that really doesn’t capture what they’re about. They have deep roots among the Palestinian population of the occupied territories, and in particular Gaza, and can be regarded as a legitimate, mainstream expression of the broader Palestinian national movement, given their popularity and success over the last three and a half decades. They have never attacked targets outside Israel/Palestine, and do not accept non-Palestinian volunteers.* That said, they do have their origins in the Palestinian branch of the Muslim Brotherhood, and so acknowledge an ideological lineage which they share with al Qaeda and many other analogous organizations going all the way back to the 1930s.
Those working in Israeli intelligence understand the distinction. However from a popular Israeli perspective there is little difference. Like Al Qaeda and ISIS, Hamas have attacked Israeli civilians using suicide bombs, mass shootings, stabbings, car rammings, etc., and now it is claimed beheadings. It seems to the Israelis that, just like with Al Qaeda and ISIS attacks on Western targets, there is no limit to the violence Hamas is willing to inflict on them.
*(edit): actually I can think of at least one possible case. In 2003 during the Second Intifada
two British suicide bombers attacked the well known bar
Mike’s Place on the Tel Aviv beachfront, and they were subsequently claimed by Hamas.