Jango Fett was probably stronger in a straight fight, while Boba Fett was more dangerous overall because of his later tech, experience, and ruthlessness.

Why Jango gets the edge

Jango was trained as a top-tier Mandalorian bounty hunter and is usually portrayed as the more naturally skilled fighter and better hand-to-hand combatant. In a pure “who wins in a duel” matchup, a lot of fan discussion leans toward Jango because of that raw combat edge.

Why Boba is still a threat

Boba had more time to grow into a veteran and often had better gear, upgrades, and battlefield experience by later stories. That means Boba can look stronger in terms of survivability, resources, and overall threat level, even if Jango may have been the better fighter one-on-one.

Simple verdict

If you mean physical combat skill , Jango. If you mean overall danger and longevity , Boba. In a close matchup, Jango likely wins more often, but Boba is the more hardened survivor.

TL;DR: Jango was stronger as a fighter; Boba was stronger as an all-around survivor and bounty hunter.