Which was better?

Both. Voyager does perfectly well before Seven shows up in Season 4 I believe, and she was the eye candy the Star Trek series had been missing since Jadzia in DS9 and Troi in TNG. Kes was eye candy to a point, and even Chief Engineer Torres, but not to the point of Seven or T'Pol in Enterprise.

I liked it better with Seven. Her ongoing progress toward reclaiming her humanity was a great arc. My only complaint was that she often seemed overpowered and her abilities leaned on a little too heavily as a deus ex machina.

I would say the show got better when she came along. But, I wouldn't say it was better because she came along. It just seems that the Star Trek shows take a few seasons to get situated.

With Seven even meh episodes had a new comedy element with Seven.

Better with.

Definitely with. Kes really didn't have the presence she did.

It was better with her. She nailed the part and her character and story lines were entertaining.

Kes was nice, but as dull as ditchwater. Even her attempts at evil were lacklustre, when she was taken over by the warlord.

The show seemed a lot better when Seven came along, although many people are convinced that the Borg stuff increased too much to the point that they were ruined.