Maybe try Colin Davis; the 50's account is the "classic" recording of this work. He did it again shortly before he died on SACD which is another excellent account if you don't mind the extreme reverberation from the cathedral he recorded in.
Berlioz himself thought this was his finest work and I tend to agree with him and this isn't due to the fact I don't like his other stuff. Compared to orchestral works I find there are relatively few true non-opera choral masterpieces; in my mind, this ranks amongst some of the very finest of them.
