I'd have to give the nod to season 1, but season 2 was not as big of a drop off as I was expecting. I liked the island stuff going on more in season 2. I only watched both on DVD though not on tv, so I started and finished it quickly and am now really looking forward to season 3.

Give me season 2. I don't care if every episode before the S1 finale was gold -- the season resolution was most unsatisfying and left a bitter taste in my mouth the whole summer. They had the good sense to do better at the finale the second time around.

I liked season 2 more.

It seems most people like season one better because it was new and we had no idea what was going on, but season 2 answered more questions.

Season 2 because it had a darker feel to it, the characters were themselves, and also the characterization really was realistic (people being good one moment, a prick the next...there were no clear cut right and wrong/black and white areas in season two). We delved more into the secrets of the island, and the ending had an Empire Strikes Back feel to it.

season one

Season one for the character development
Season two for the plot development

Season one gets the edge because without characters we care about no one would care about the plot.