El Goonish Shive has eight main characters which allows them to run the gamut of the scale. However, Susan is firmly cynical and Tedd is probably the most idealistic. Which makes their Odd Friendship what it is.
In City of Reality the titular city is so firmly embedded into "idealistic" end of the scale, it's actually kind of creepy, to the point that you might think of it as a deconstruction of the concept itself. In fact, it's even noticed by some of the characters, and made into part of the plot. Later, however, they face inhabitants of the other worlds in the universe, which tend far towards the opposite end of the scale, showing them just what they're fighting for. And against, as their main opponents for Chapter Five turn out to be some of their own people, turned Well-Intentioned Extremist as they attempt to protect Reality's way of life at any cost.
Chess Piece is somewhere in the middle, veering either way, though characters themselves range from idealistic (Vlad, Kwan, Diligence) to in the middle (Sam, Doug, Skulker) to cynical (Doug again, Danny, Abe).
In a similar manner, The Game Master in DM of the Rings is the only one trying to uphold some sort of idealism. This crumbles slowly as he becomes fed up with his extraordinarily-cynical players.
In Harkovast, a lot of the tension between the characters come from those that are more cynical (Shogun and Ki) and how their attitudes conflict with those that are more idealistic (Chen-Chen and Sit Muir).
8-Bit Theater appears to be one of the most unabashedly cynical things ever drawn. For example, Black Mage's super nuke attack, the Hadouken, is powered by love. As in: every time he uses it, the divorce rate goes up measurably. However, it's too silly to be considered either cynical or idealistic. The Light Warriors, BM especially, are the universe's butt monkeys and anyone they come into contact with gets hurt, but there are genuinely good guys in the comic (Fighter, WM, the four White Mages at the end), and it's all Played for Laughs.
Polandball is all over the place regarding this trope. Most of the time, many strips tend to fall into the cynical side, often exposing many nations’ shortcomings as means for satire. However, some other strips also show that they can be decent individuals and their actions are genuinely for the greater good of the world.
Jack sits oh so very far on the cynical side, possibly up there with Warhammer 40,000. Half the premise is: "If life's not fair, why should the afterlife be?"
Homestuck comes off as a mixture of both sides. On the one hand, the game of SBURB seems to award victory to those who grow up and face their fears and so on, resulting in a fairly typical coming of age set up. On the other, for the trolls, 'coming of age' consists of succumbing to their innate bloodlust (and by NOT murdering each other they end up losing) , whilst the kids are stuck in a universe doomed from the start.
Basic Instructions is reasonably far over onto the cynical side, as it's full of snark and many characters are distinguishable by their flaws. In many ways, it's similar to Dilbert in terms of cynicism.
A Miracle of Science is on the far idealistic side. The whole point of the story is that mad science can be cured without using any violence. Then there is Mars, which shines in idealism with its utopistic society, and even the crime-ridden Venus is relatively tame.
Surprisingly for a webcomic set in a post-apocalyptic world, A Moment of Peace is pretty idealistic. Despite the world being full of monsters, the main characters live very cheerfully wandering around, and they even befriend some monsters.
Roommates is an interesting case. The characters are if not cynical but at least snarky and disillusioned. The world on the other hand is a World Half Full that at least gives idealism a chance and where The Power of Friendship actually works (finding friends being the harder part of the equation).