I believe Raw is the superior brand. Honestly, I can't even watch Smackdown half of the time. I have more important things to do on a Friday night. But I guess I'll actaully give some reasons.
Storylines
I find the stories told on Smackdown to be quite ridiculous most of the time. With the exception of the Kane Search going on right now, I have no interest in anything else. Even said storyline kind of bores me, the only saving grace would be that Kane isn't the culprit in the end. If he is, however, then it will be a total letdown.
On the other hand, the NXT angle going on right now has had me thoroughly enthralled the past few weeks, along with Randy and Edge's program, and seeing the different guest hosts making asses out of themselves. Maybe I just like watching the established stars do what they do best as opposed to watching rookies stumble along the way, but that's my thought.
Psychology
Smackdown does have some entertaining matches from time to time, but I find them to usually be quite spotty. I prefer the use of Psychology in a match, and Raw is way more dominate when it comes to "Ring General" type performers. I love watching the likes of Edge, Jericho, and Orton wrestle well, just about anybody.
Production
The fact that Raw is live every week just adds to the atmosphere of the show. There are no retakes if someone fucks up an ending or an intro. Just watching Smackdown feels kind of bush league, it definitely lacks the the flare that Raw has.