MCU Widow all day long. Comics... Widow for slight majority. Remember Natalia also has the Red Room's equivalent to the super soldier enhancements and partial Hand enhancement (childhood circa 1941, Madripoor). Bobbie has a derivative of the infinity formula.
Widow might/probably wins.... I feel Nats gadgets and equipment gives her the edge and yes a Baby Girl Bobbie has superpowers and is a great fighter I feel Nat has handled people who are far more superior i strength and she took something is the past but it made her peak human,not superhuman like Bobbi. But it could go either way.