If you are looking for a high performance 40Gb drive, then there is no reason to consider either the Seagate or Maxtor. The new IBM 120GXP (available in a pricy 40Gb version) trashes both in regards to performance. Of course, as far as acoustics (low noise) goes, there is still nothing even close to the Seagate Baracuda IV. According to Storagereview's tests, the Maxtor produces 5dB more than the Seagate, which makes it virtually twice as loud (there is a doubling in noise with every 6dB increase).
Of course, if you want the absolute best ATA performance available, look no further than the 120Gb Western Digital WD1200JB (the version of the WD1200BB with an extra 8 megabytes of cache); unfortunately, at $250 from Googlegear, this drive isn't cheap. IMO, however, for the significant and noticeable performance gain you get over the Seagate and Maxtor, it is worth it. I could not tell any difference in moving from a 1540MHz Thunderbird to an Athlon XP @ 1840MHz in applications, but I noticed a massive difference in moving from the Seagate Baracuda IV to the Western Digital WD1000JB (which is slightly slower than the WD1200JB).