MD:
-MZ-N510: AA battery, remote port, optical in, AA battery. Alas no mic-in.
-MZ-S1: excellent build quality, but too bulky and only Type-R
-MZ-E720: Very nice design and color (I have the brown one
), HD-amp, but no Atrac Type-S
-MZ-NH900: HD-amp, mic-in, wheel control, can record in classic SP, but no MP3 support, limited LCD display
-MZ-DH710: HiMD, MP3, AA battery, scroll wheel, but downloader only
-MZ-RH910: HiMD, MP3, AA attachment, mic-in, but adulterated MP3 playback, LCD although larger than previous gens, still feels cramped and small
-MZ-DH10P: Color screen, screen can display kanji with service mode hack, digital camera, but very slow disc access for digicam purposes, and the fact you need service mode hack to enable kanji display
-MZ-RH1: Unadulterated MP3 playback, metal, mic-in, HD-amp, spectrum analyzer!, very slim recorder, the only MD/HiMD unit that can upload legacy recording, but cannot display track title on the unit's OLED screen and no AA attachment
Flash player:
-NW-E3: nice design, backlit LCD, metal body, spectrum analyzer!, but only 60MB, Atrac3 only, no kanji support, and very poor battery life
-NW-E99: good design, backlit LCD, support all Atrac3+ bitrates and MP3, AAA battery, display support kanji and even korean, ability to shuffle by albums, but USB1.1, surface smudges easily, and 512MBx2 instead of 1GBx1.
-NW-E005F: USB2.0, OLED kanji capable display, tactile buttons, but noisy headphone out, no gapless with AAC, loose resume position after charging with AC adaptor, cannot shuffle by albums, significant battery discharge when "off"
-NW-S705F: Nice stock bud, built-in N/C, gapless AAC!, OLED kanji capable display, but useless album art display, cannot shuffle by albums (c'mon Sony, the E99 can do this), porpietary WM port
On all of them, 1 biggest con is Sonicstage. Yeah, it is more usable now for transferring tracks only, but it's 2007 now. Sonicstage is not even unicode.
Now happy with iTunes + iPod: unicode support, gapless MP3, smart playlist.