Stick with what fits for you, madness can pull a lot more dps in longer fights, but it's a lot harder to learn than deception. My recommendation is to start out with deception as a main spec, but practice madness if you think it's interesting. Change specs when you learn via parse that you do more dps with madness.
I disagree, because madness is a harder spec, I'd say do that and learn it now. It's far simplier at early levels to learn a spec piece by piece. Hit a new level, add this mechanic. At level 50, it's tough. I tried to change my spec to madness, but all the dots (lightning charge, creeping terror and crushing darkness)+the procs (Raze, Exploit weakness and unearthed knowledge) as well as managing only 100 force was a bit much for me.
Maybe I got greedy having both exploit weakness and unearthed knowledge, since I hear the build is good without either, but it was too much for me to watch.