I tried Poppy a couple times since she's free this week. Did rather poorly, although I was only with two pals which meant we kept having to deal with shitty insta-lock midlane Kennen's. First game also had a jungling Amumu who acted like a typical shittalking pub and didn't help anyone. Second game we had a jungling Irelia though who was much better.
At any rate, Poppy seems like she could be incredibly strong if you get your items for her, but she has trouble farming due to a lack of spammable abilities or AoE, which means you probably need to be killing enemy champions to get the gold you need. Overall probably not my kind of champion.
Urgot on the other hand, 10/10 would Q again.
Poppy is, like Tryndamere, an Assassin/Anticarry/Herpaderp.
Her goal is to charge into the enemy team, drop her diplomatic immunity on someone with no CC, kill every squishy she can get her hands on in 6 seconds, and run or die.
I believe the generally accepted consensus for best ranged carry is either Ashe, Miss Fortune, or Corki. Almost always you will see one of those three in a team in tournaments and high level games. Rare to see a Tristana actually. But I agree she is considered the guiding point.
I think the reason she's rarely played is that it's actually relatively difficult to lane with Tristana, especially if you compare with Ashe or Miss Fortune who excel at laning (harassment + last hits). Both of those have a reliable cc ability too, which make ganks easy to pull off whereas Tristana has only her buster cannon. And we all know how well buster cannon works as cc (lol, I shot them back into their tower sorry). In other words, Tristana defines the ranged carry aspect as she scales the best out of the.... five ranged carries in the game (Ashe, MF, Kog, Trist, Corki) but just like Master Yi... she's pretty crap until late game. But if she's fed, then just like Master Yi, she will dominate everything including the other ranged carries.
Ashe and Miss Fortune have better harassment and can handle NOT being a solo lane better, at the cost of worse escape potential (MF drops a Make it Rain and prays she can get away while it still slows, Ashe spams volley and slow-shots backward as she runs, MAYBE dumping her ult). The thing is, with a good enough team you won't always need that escape potential.
Buster Shot, like Anivia's wall, requires a great deal of skill and maneuvering to use properly. It works best when you (a) rocket jump or flash past them, (b) drive them at an angle into a wall, (c) break the enemy positioning at the start of a fight (e.g. everyone follows their Shen in, then suddenly Shen is behind them. Hi squishies. What's up. Also you can combo those applications as you wish if you coordinate with your team. Their tank initiates, your team rushes them, you hop past and blow their tank out the back). You should not use it to finish champions off; it only results in them getting away most of the time. Also your autoattacks should do more damage by late-game.