I voted Kirk, but it's something of a comparison of apples to oranges to kiwis to grapefruit to prunes.
We get to see Kirk at least twice in scenarios that are really well sold as quasi-realistic tactical situations; we aren't just told how great he is, we are actually shown it.
This is less true of Picard because while we're told that he's great, TNG had little in the way of convincing space battles, and during the major exception he was assimilated by the Borg. Picard was really more convincingly presented most of the time as the kind of leader who knew that winning without fighting, rather than fighting to win, was the acme of skill.
DS9 had plenty of battles but mostly presented Sisko's core skillsets as being in scheming and counter-scheming, intel and counter-intel work and sheer testicular fortitude. He was like Picard with a streak of pure ruthlessness underneath. A fine character but his greatness wasn't really in battle tactics as such.
VOY and ENT both make cases for their Captains to be great tactician, but in Janeway's case it's because the Borg have been thoroughly nerfed by the time she encounters them, the moreso yet when they turned oup on ENT. Victory-by-writers'-contrivance doesn't really count as great tactics.