Which installment of the Heroes series had the best campaign storyline for you?

I liked the Campaigns in the third one most of all — coherent, interesting campaigns with a good plot, which for example I didn't notice in the 4th... I won't speak about the second one, as I didn't complete the campaigns entirely... And it's no coincidence that Heroes Chronicles was made in the third one, although I don't deny they didn't do them for subsequent parts, apparently considering the experiment not very successful...

Chronicles is a miscarriage in the M&M universe. Mind you, the plot of the 4th's campaigns is very interesting if you read more than just the mission descriptions and the victory and defeat goals.

And what about the second one with Archibald and Roland?)

Roland appears a lot in AB, and his character and texts are very well developed there; in general, you read AB like a book (as is the case with the 4th), while Archibald is prominent in M&M7.