Doing either will certainly help build strength; I think you can find as many experts (or, "experts" ) that will come down on either side as the best technique, but my non-expert advice would be to try both, see if either one jumps out at you as really doing you more good.

I tend to do the low rep, go to as close to muscle failure as I can, but if I get the urge, I'll lower the weight, and do a buttload of reps. Change can be good.