I may not be the BEST source for this, since my main concern is powerlifting, but my lower back is pretty well developed, so I'll throw out a little advice. I keep conventional deadlift reps very low for almost all training sessions. Once every month or 2 I may hit a max rep set of 10+, but for the most part, I keep my reps at 5 and under, and generally pretty heavy. I also keep total reps in a session to about 15 or less. I deadlift once a week.
I do RDL's with less weight and higher reps. Maybe like 3 sets of 10. I think working with some combination of the 2 styles would be beneficial. I also know a lot of people who don't really believe deadlifting from the floor is necessary, so if you prefer rack pulls, I don't think that's much of an issue at all. You can go very heavy on those as well, and definitely pack on some thickness.