I like the Mackerras Brahms quite a lot as well. To me, Mackerras is a seriously underrated conductor. He has made a lot of really fine recordings. And the Telarc audio on the Mackerras set is very good. Much better than the Abbado set. The Abbado set sounds congested, thick, lacking in transparency. The inner voices are not revealed very well. Of course, it is DG. They liked that "wall of sound" effect back then. I'm not always a fan of HIP, but Makerras makes a good case for Brahms played that way.
On the other hand, I do love Brahms played bigger than life. I don't really care how the orchestras back then sounded. If composers back then had at hand the instruments and musicians around now, they'd have not hesitated to use them. So, as far as I'm concerned, the opening and finale of Brahms 1st - the bigger the better. Blow my hair back and glue me to my chair with audio G-force. Make pretty in between, but make monster music at the edges.
I have an old video of Ozawa and BSO playing Brahms 1 in Japan. It may not be the most elegant Brahms ever performed, but the electricity in that hall is just magical, and the BSO play their collective butts off. By the time they are done, fingers and lips are bloody. Probably sounds like crap on CD, but watching that video is so much fun, who cares.