An ep of 24 is like a Lays potato chip. You just can't have one. CSI is Quincy with a larger ensemble of key cast members and a Columbo-like gimmick for solving crimes.
If you get 24 and don't like it. You are clinically insane.
Both season's Look great. The Show itself is fantastic. And Season 2 has some great extras. Costco has season 2 really cheap until tomorrow (I think $25)
Ugh, I'll give me two cents, I'm sure not everyone will agree. I would say buy only Season 1 of 24. While Season 2 was good, it seemed less plausible, and was a bit too 'overblown' thanks to it's expanded budget. (Mind you, I liked it. But as I'm watching Season 3, I can really see the producers and writers stretching for ideas, and frankly I saw a lot of that in 2)
CSI, however, is still VERY strong after 4 years, and very easy to get into. It may be easier to watch as the episodes are very independent in nature. Tho, Season 2 of CSI is much better then one.
So I will say buy Season 1 of 24, because it honestly was the best first season of any show (sans the Sopranos) that I have seen in a while. However, the later seasons are quite overdone. CSI is very strong in Season 1, but 2 is excellent. Essentially it all comes down to what you want to see: An Action show? Or a detective show?
Also as a DVD edge, I would give it to CSI Season 2. It's widescreen (finally) and the 5.1 mix is AMAZING, better then some movie mixes. The mix on 24 S2 was quite disappointing to me, as it was no as emersive as the CSI track.