Eh I'd say Season 2 was the worst Wire season. Season 5 felt a bit rushed but I thought it had the shows strongest episode (the last one) and I thought it explored one of the most interesting aspects (the Media).
Season 2 grows immeasurably the second time round (I don't know how many times you've watched the series). At first the new cast and setting is a bit jarring after a season of getting to know all those charismatic gangsters in season 1, but in some ways it's the cleverest and subtlest of the Wire seasons. It also has the
best use of music of the entire show.
Season 5 is great, but I just feel they jump the shark very slightly with the McNulty storyline. Not enough to spoil the show by any means, and in fact, it's almost comedic watching it all unfold, but it doesn't have quite the same power as previous seasons, so I'd definitely rank it last of the 5. I also think the media wasn't explored as well as earlier sections of society were in previous seasons - probably due to the 10 episode season - we just don't get attached to the new characters as well. I agree that the last episode (and the penultimate one, which may have been even better) were some of the entire show's best though.