Hitachi are good, and as far as the amiga is concerned, it doesn't care if its UDMA33/66/100/133. the drives have to support PIO mode 0, which is what the amiga uses, to be able to boot in the first place, untill what ever OS sorts out its chipset drivers to support the higher speed modes. thats my understanding.
have had no problem accessing a 20Gb UDMA133 and 100Gb UDMA100 drive on my os 3.0 A1200. just a shame that the 3.0 roms would only allow me to see the first 8gb of them :/ but then i'm not sure if that was a FFS problem or a rom problem. :-)