Take That are definitely the best. They have some fantastic tunes and their live show is excellent. Also they all have input into the band and Gary is a great songwriter.
Boyzone are piss poor. They had a couple of songs in the 90's I liked, the rest was pretty bad and that song Love You Anyway is atrocious...not to mention the video *cringe*. Their shows are awful as well judging by the clips on Youtube, dancing and singing is crap and their performances come off as cheap and cheesy, I saw a clip of them dancing with toy guns how woeful.
I hate Westlife's songs, but in fairness they have at least 2 good singers, Mark and Shane, and I think they're better performers than Boyzone.