It depends on what we're talking about. In terms of the better person, Carter is clearly better. However, LBJ was a far better President. In terms of their presidencies, I wouldn't mind seeing LBJ's domestic policy combined with Carter's foreign policy. Vietnam's the obvious mark against LBJ. With Carter, I've always found his domestic policy accomplishments to have been severely lacking, especially considering the huge majorities Democrats had in both Houses during his Presidency (including a supermajority in the House during his first two years).
That's because he was a Southern conservative Democrat (a nice one though, with good intentions) and he wanted deregulation and more people working, which did not go down well with the Democratic left like Ted Kennedy. He had some good achievements (as a result of deregulation rather than creation of programs), that are now so normalized that it's hard to remember he was the one who got them going. He certainly doesn't deserve the ultra-liberal image painted by conservatives, except maybe for creating the Department of Education, trying to broker peace treaties, and making human rights a plank of U.S. foreign policy, especially after the realpolitik of the '60s and early '70s.
In a way, Carter is like the anti-LBJ.