I thought the Super Outbreak on April 3-4, 1974 was the worst
138 confirmed tornadoes over 13 states
Lost my grandmother in that one
In terms of the number of tornados, that’d likely qualify. The 1925 event comes out on top (considerably) for fatalities and (estimated) intensity of the primary tornado.
A lot of the fatalities in the Tri-State tornado were caused by masonry construction(s) of schools and such, which buildings might well have mostly survived an F3, but with an F5, those multi-story brick walls collapsed onto sheltering people, and likely many bricks became projectiles too...