You can think of the active Pentas as a Beolab 150 sandwiched between the bottom plate and the rest of the speaker (you can actually remove it and end up with a Beovox!). Apart from the empty space behind the display window on the passives, the actual speaker columns are identical and so have the same pros and cons including midrange foam rot. I think there are minor differences in the crossovers, though, to keep in mind when ordering replacement caps (see my thread on the subject, I will continue it when I get my new caps).
The Beolab 150 might be a better amp than the Beomaster 6500 but apart from that, I don't think the actives could have much of an edge over the passives - they still have only a single amp and a passive crossover, unlike the later Beolabs.
One thing I haven't seen discussed about their respective merits is that with the actives, the "sweet spot" for listening is some 20 cm higher because of the amp down under. The Pentas are rather directional vertically, and the passives are best enjoyed on a rather low seat or sofa, unless you can sit far away from them.
Someone else can discuss the differences between the various active versions, I always forget which was which...