That's funny. I have played CB's and Al's several times. Comparing the two is fun. The truth is CBGB's is the best sounding dive I have ever seen. The acoustics are great and the since of history makes you feel like every gig could be something special. The great thing is that it actually could be the start of something. The contacts we made there helped me for years to come.
Al's on the other hand is a great place to get that Bukowski LA vibe going. The blocks around it are not as scarry as the Bowery can get but you are actually in more real danger. Playing Al's will do nothing for your career but it is a must do for anyone that thinks they're hard.