I've only ever watched the second series. And somebody has lent me the second series to watch again.

It's absolutely bloody amazing, and I WORSHIP the following characters: Jack Bauer, Michelle, Tony Almeida, El Presidente, Kate Warner, Lynne. Is it not the best cast, ever? Isn't it? It is? It is.

cheerio!

I think the second series was my favourite out of the 4.
It was the first one I watched - I missed the first one completely when it was on TV, but after watching series 2 on TV I bought the first series.

The first two are in my mind definately the best.