Just out of curiosity, are most of the people who are saying "infernal affairs" is better than "the departed" Asian?
Im Chinese by the way and i thought Departed was better. However, I think it really depends on if you grew up in an American or Chinese society.
I'm English and saw TD first, several times!, before watching IA, and can say IA is better to the point where I can't watch TD the same way now.
Everything good about TD was basically copied from IA. Everything in TD that didn't quite work happened when they tried to do their own thing (eg, the "love triangle", the whole FBI informant story etc). It's also implausible that DiCaprio's character would be in so deep with that crew in a matter of weeks - in IA, it takes him 9/10 years and several other bosses to get to that point, which makes a lot more sense. Also Jack Nicholson just murdering a couple of mafia guys with no repercussions - on the contrary, the mafia backing off - was beyond suspension-of-disbelief.
The only thing TD has over IA is the banter/one-liners. That said, I get the impression the UK subtitles are only giving the jist of what's being said, and maybe the sense of humour wouldn't translate anyway - Cantonese speakers might find IA superior in this respect too.