Can't say which is better, both are very good, and each appeal to a slightly different taste. In terms of amplification, both have very good output. Yamaha has more features, but I'm not a feature kind of person. I personally prefer the sound of Marantz for music. I have heard the 2400 with similar speakers to mine (smaller, but same drivers), and I felt it sounded very good. I am running a Marantz 8300.
What kind of speakers will you drive with this receiver?
I have Klipsch speakers, which IMHO have a very balanced and 'active' sound when driven by my Marantz SR7200. I demo'd a Yamaha RX-2200 a while ago and they made the Klipschs sound bright. The Yamaha did not bring out the best qualities of my speakers.