Horowitz has more bad recordings than Argerich but also more great recordings. A conclusion from that, in my opinion, is that Horowitz is more inspired than Argerich but is also a far less reliable technician.
To give a few examples: Horowitz in Chopin Mazurkas, Scriabin (pretty much any), early Liszt Sonata, Mendelssohn Variations Serieuses, Schumann Presto Passionato, transcriptions, all of his post 1985 recordings...are all interpretations of incredible inspiration that are hard to find counterparts of in Argerich's catalogue.
Then again, Argerich is a vastly superior chamber musician. And her Bach is a lot better than Horowitz's would have been, in my opinion.
Also, this comparison is pretty arbitrary.