Well, since lemmy is sparse with actual historians, and "bigger" is pretty vague, ima chime in since i was alive and aware for both. All anecdotal at that!
In terms of news coverage, I would say that they were equal for their eras. OJ saw the birth of the 24 hour news cycle, and thus likely had more raw air time across all sources. But you couldn't escape the McMartin trial within the scope of the time. It got steady coverage by all the major networks, plus the rest during the earliest phases. That decreased over time, with only major events reaching air or print by the last year or so.
However, it could be argued that the social impact of each was comparable too, though I think the sustained "satanic panic" side of the McMartin snafu might tip scales that way, since it lasted longer than the shock of OJ's Bronco ride and subsequent trial
There's no comparing the price tags though. The McMartin trial was the most expensive in us history last I checked.
In other words, it's a damn close race for "bigger".