I had a friend ask me this question a couple of weeks ago, and it's a difficult one to answer. But if I were to choose a favorite season, I'd have to say that Season 1 is my favorite. I love the original Barksdale crew. Avon, Stringer (who wasn't working his own agenda at the time), Wee Bay, etc. etc. That original crew would've wiped Marlo and his crew out.
I loved seeing the maturity of a lot these characters, Bodie being one of those that really sticks out for me. The first season he is just a kid who I couldn't stand and by season 4 he became one of my favorites. I was really pissed when he was killed. That last scene with McNulty was one of the best. "I feel old." When he said that, you could just hear the weariness in his voice. He started out as an obnoxious corner kid and matured beyond his years.
I loved in season 5 seeing Poot working a legit job at a shoe store. I don't blame him one single bit for getting off the corners. And of course, one of the biggest changes was Bubbles. What a journey his character went on. From being an addict shunned from his family and society, to cleaning himself up, taking responsibility and slowly gaining acceptance from his sister (the open door at the end).
The ending is one of my favorite scenes, you see how in Baltimore, the cycle repeats itself. Omar is killed and Michael becomes the new Omar. Bubs cleans himself up and Dukie becomes the new Bubs. Slim Charles basically becomes the main man after patiently waiting in the wings.
What a great series!