Smoking weed
(note that these are personal observations from both smoking weed and seeing others smoke weed)
Pros: None that I have observed, I pretty much sat in one spot for 6 hours straight doing nothing although some people claim an increase in creativity.
Cons: Illegal in most places, makes you dumber (or at least look that way), awful taste, reduces motivation to do anything, expensive and profit usually funds further criminal activity.
Summary: If you enjoy the high and only partake occasionally, go for it. I did not enjoy the high and will be sticking to booze and tobacco.
Cigarettes
(note that I am an avid smoker and thoroughly enjoy Camels, don't expect an unbiased opinion)
Pros: Enjoyable flavor, stimulant, not a debilitating high, comes in filtered packs, legal, and can be a social tool.
Cons: Addictive, unhealthy, expensive, profits fund an evil corporate empire.
Summary: If you enjoy the flavor and don't mind wrecking your lungs, go for it. Also useful to break the ice in conversation and have something in common to talk about in social situations.