I prefer Rockstar, but LA Noire's open world really sucked. Good game, but the the film reel hunt was boring, the car collecting was boringer, there was only one radio station (The Bickersons were hilarious, though), limited song selection (how freaking expensive can it be to license Louis Jordan / Cab Calloway / Andrews Sisters songs?), landmarks were glitchy and weird (who cares about the goddamn bagel factory?), didn't download the "badge pursuit challenge," and you couldn't shoot random people, not even in free roam mode. Obnoxiously shoving people and backing over your partner with the car door remained fun, however.
Rockstar wins on the basis of three games, though. Vice City, San Andreas, and Red Dead Redemption. That game was simply gorgeous, had smart and fun fetch quests / survivalist challenges. Bethesda is good, but their open world IS the game. Rockstar games feel like there are multiple levels of "reality" to it that make the world feel fresh and different.