I've heard a lot of things about both engines. I know alot about both because I'm a Toyota/Nissan fanatic. The rb26 (from what I've seen) can get more hp when built to the max but is extremly unstable at that point and will need extreme work after about two quarter-mile races. The 2jz (from what I've seen) can't get up to as much hp but when maxed out the engine stays strong and doesn't need as much work.
Highest hp 2jz I've seen: 1600 hp (aap). Highest hp rb26 I've seen: 2000 hp (some video on the internet).