I know I'm late as hell but started watching this show recently and had to rank em...
Season 1 - The first one was the best because it was our introduction to this world. Stringer and Avon were so good. Every scene in the pit was excellent but especially the chess scene. Unbelievable.
Season 4 - Hard not to rank this the best. Every story line was so perfectly crafted. Definitely the most emotionally draining season, as well. They knew exactly what they wanted to say with this season: some kids are born into the game... they can't escape it unless it's in a body bag. They did a masterful job of saying just that.
Huge gap
Season 3 - This season felt like a setup for season 4 and not much else. The only storyline it saw through was "Hamsterdam" which wasn't that interesting to me. There were also times where it felt unrealistic, like Avon shrugging off his cousin's murder after one scuffle w/ String.
Season 2 - This season at least had complete storylines, but I just can't get over how annoying the younger dock workers were. Ziggy is The Wire equivalent of Jar Jar Binks. I didn't find Holly from The Office or her character particularly interesting. Frank Sobotka was excellent, though.
Season 5 - Haven't watched yet but sounds like I'm gonna hate it..