I seriously do not think that Zhang Fei was a drunk. The novel made him a drunk head, but he is indeed not a drunk historically.
I would rank Zhang Fei as the top Shu general because he was the only one who was really rough yet had a soft spot for gardening and drawing apparently. Zhang Fei is a true strategist in my mind. He has rarely came up with a strategy during battle that failed.
Also I would like to point out that he’s one of the very few men that managed to defeat Zhang He, a feat accomplished by none other than Cao Cao and Wang Ping.