I prefer single concerts all the way. At a festival, the bands have to play more or less limited setlists, as only the headliner/closing act can expand with several encores.
Also, at festivals the acts will mostly play only their most famous and commercial songs, because they can attract new fans there, while at a gig they will play a mixture of classics and more alternative material as only real fans that know the band's work entirely will show up at the concerts usually.
Thirdly, at festivals there's a mixture of people, while at concerts everyone in the crowd is into the same band and same style of music, which makes it very easy to make contacts with other people. You immediately have a point to start from, you have something in common after all: love for the same band.
