Structuring D&O Insurance Programs: To Layer or Not To Layer

As more D&O insurers and greater capacity enter the D&O insurance market, many insureds are reexamining an age-old D&O insurance issue:  is it better to place an entire D&O insurance program with one (or a select few) insurers, or is it better to place a D&O insurance program with multiple insurers?  In other words, should a D&O insurance program of a given size consist of a few policies with large limits of liability or numerous policies with smaller limits of liability?