Who was on which ship?
While we know who the passengers on the Mayflower’s voyage to the New World were from William Bradford's list which he compiled about 1651 (over thirty years later), and we know that some of the passengers on the Speedwell stayed in England after the ships turned back, there is no full separate list of original passengers on the August sailings of the Speedwell or the Mayflower. There was no passenger manifest for the two ships that has survived, or even for the Mayflower itself for its voyage: after all, who would check the manifest or passenger list once they reached Massachusetts? The only list of passengers is the one compiled by Bradford in 1651 for Of Plimoth Plantation, for those who had made the 66 day voyage to Massachusetts.
William Bradford and his wife were almost certainly on the Speedwell, as shown by his account of the embarkation; likewise, Edward Winslow’s full account of the embarkation (“Hypocrisie Unmasked”) also suggests that he and his family were also Speedwell passengers. William Brewster and his family were likewise probably on the Speedwell.