B7: Blake was the lead for the first 2 seasons but even then Avon was still a major character, some would argue *the* major character. After Blake's departure, Avon became the lead.

B5: Arguably an ensemble show all the way through, just with a shift in major/lead character after season 1 and, if some of the rumours are to be believed, Sheridan was really following Sinclair's original storylines.