I think I would have to say the best decade for Spider-Man is the 80s. It breaks down as follows:
60s: Debut, Stan was at his best working with strong artists like Ditko and Romita. The majority of memorable villains and supporting characters are introduced. Spidey has only 1 title with some guest appearances. The drawbacks are that Stan’s dialogue doesn’t age that well and there is not much material to choose from outside the main title.
70s: Spidey becomes more ubiquitous with Marvel Team Up and Spectacular Spider-Man ongoing titles. There is also the children’s title Spidey Super Stories. Stan steps back from writing, so we get runs from Conway, Lein, and Wolfman. Stories get darker with the deaths of George Stacy, Gwen Stacy, Norman Osborn. Villains such as Morbius and Hammerhead are introduced. Supporting characters Punisher and Black Cat first appear. The weaknesses are stories become darker, Peter mopes a lot even as Spidey, and there are many forgettable stories, especially in the ancillary titles.
80s: A lot of well regarded runs in this decade. Stern, Defalco, Michelinie on Amazing, Mantlo and PAD on Spectacular, DeMatties on MTU, and Michelinie on Web. Villains introduced include Hobgoblin and Venom. Peter and MJ married. Conway returned on Web and SSM. We got classic stories like Kid Who Collects Spider-Man and Kraven’s Last Hunt. The black costume is introduced. Romita Jr., Frenz, and McFarlane are on art. MTU ends and becomes Web. Drawbacks include the editorial mess-ups that resulted in Defalco/Frenz fired from Amazing, the muddled conclusion to the Hobgoblin story, the rush into the marriage with minimal buildup, and creative teams in a flux that necessitated a lot of fill in/inventory stories interrupting the ongoing stories.
90s: A fourth title is added as McFarlance starts writing. Larsen and Bagley join as artist. DeMatties writes Spectacular, then replaces Michelinie on Amazing. Mackie begins writing the character. Ancillary titles come and go as Web turns into Sensational, Untold Tales and the quarterly Unlimited and Team Up all begin and end. The decade ends with the Amazing and PP:SM are relaunched. Drawbacks include the poor reception to Mcfarlane’s writing, forgettable runs like Kavavaugh, the Clone Saga taking over the main titles for two and a half years with its bloated stories, never ending mysteries, and editorial driven directions. The titles took a big hit after the Clone saga, struggling to regain its audience. This culminated in the relaunch that was not well received. My choice for the worst decade of Spider-Man.
00s: Mackie ends his run. Jenkins writes some nice stories, JMS rejunenates the title. Decent runs by Millar, PAD, and Aguirre-Sacasa. JMS ends his run with the controversial One More Day that ends the marriage. The ancillary titles are cancelled as Amazing goes to 3 times monthly with rotating writers. Brand New Day resets the status quo, bringing back supporting character and introducing new villains.
If you’re a marriage fan, then OMD and subsequent stories are the worst ever with Spidey ruined as a character. If you’re not a marriage fan, then BND revitalized the character and title. Drawbacks include the end of Mackie’s lackluster relaunch, and if you loved the marriage, OMD and everything after.
10s: Slott goes from rotating writer to sole writer (with periodic assists from Gage). Ancillary titles are slowly brought back. Big Time allows Peter professional success. Superior Spider-Man begins amid howls of anger and ends winning over most of the readers. Peter comes back as the head of his own company. Drawbacks are if you are a marriage fan, you still hate everything since OMD.
Overall I’d put the 80s up as the best decade. There were multiple writers who had classic runs. There were classic storylines. Exciting new villains were introduced. There were some weaknesses, but the successes vastly outweighed them.
Next I’d put the 60s due to fact that Stan and Steve/John created great stories and characters with few, if any, missteps or poor stories in there. The only reason it’s not top is dated dialogue and low amount of material.
00s-10s are next. This is more subjective since I have enjoyed the title since Brand New Day and going forward, while marriage fans would probably put this at the bottom.
70s: Not actively bad, but it did get gloomy, and it felt like the writers were just copying Stan instead of putting their own voice on the character.
90s: The worst decade. There was still good material coming out, but you had to go to the ancillary titles like Untold Tales or Team Up for a lot of them. The Clone Saga could have been good, if it had been planned better and not stretched out. But it was abysmally planned and stretched out for far too long.