Personally, I like watching 3 the most. You had a drug cartel, a drug war, AND drug legalization. String vs. Avon's, Omar and Mouzone, and Jimmy was still butting heads with his bosses. The Bunk and Omar story was also pretty good
However, I can't even knock you for saying that about season 4. My favorite character is probably Michael Lee, and he starts getting gully in 4. First sign, when Marlo was handing out money, asks him if he's too much of a bytch to take it, he looks up like "You say something bout me?" Like he ain't even care if it was Marlo, he was just reacting. Then that training exercise with Chris and Snoop, foreshadowing?
Finally (I think last episode of 4), when Marlo sees Andre's ring.
Andre -> Marlo -> Omar -> Officer Walker -> Michael
That ring and all the jackmoves that it's spurred, and Michael ends up with it. It shows Michael at the top of the food chain, and as far as Marlo knows, he coulda taken it from Omar.
Also, Carver also becomes decent police.