Each is bad in its own way.
Bronze: Rock Bottom - Very weak mechanics, next to no teamplay, toxicity usually just comes from 1 player while the rest are either silent or being nice because they are new to the game. Wards are non-existant. Easy to 1-Man Carry out of. If you're stuck here, you kinda deserve it to some extent. You've got a long way to go.
Silver: Hell - Toxic above all else. Mechanics have improved, teamplay has not. Cooperation is non-existant. Higher abundance of trolls & smurfs. Very difficult to 1-Man Carry, as your teammates will spend more time typing than following your leadership. If you're stuck here, I don't blame you. It's kinda the equivalent of Death Mountain in Zelda 2.
Gold: Oasis in the Desert - Much more relaxed than Silver. Mechanics are even better, teamplay is becoming a thing, people are warding a lot, and flaming isn't as intense. Trolls and smurfs aren't usually found here. If you're suck here, you're basically just taking a breather. You've just destroyed the first Death Star, and Yoda is training you for the fight ahead.
Platinum: Purgatory - Imagine Silver, except people can kick your ass much harder. Personal mechanics are pretty much perfected, yet teamplay has gone to shit again. Flaming is up, smurfs are up, and trolls are up. However, people are usually on an even playing field in terms of skill. Warding is also greater. If you're stuck here, I don't blame you. Just keep trying, and you'll eventually get to Heaven.
Diamond: Senior Year - This is basically a repeat of Gold, except more challenging. Teamplay, warding, and mechanics are all up, while flaming, smurfing, and trolling are all down (but not out, just a warning). If you're stuck here, be proud of yourself. You've accomplished what the large majority of the playerbase cannot.
Masters: Graduation - You've basically mastered the game, and are rotating in-and-out of Challenger/Diamond.
Challenger: Full Time Job - Yes, you're the best in the region, but you gotta keep playing or else you're gonna get kicked out.