I have tested several portable audio recorders, as well as my Juicedlink CX231 preamp.
Test: Recorded a simple audio test to the devices below using a Sennheiser MD46 interview microphone.
Microphone held at about 4 inches from my mouth during all tests. I have normalized peaks from all audio clips to -12db, for some this meant lowering them slightly, and others such as the Juicedlink, this meant raising them quite a bit.
On several recorders I had to max out the gain on the device to get close to achieveing -12db on the device. The Marantz was one that came to mind that I could have gone higher on, this device has superior preamps to the other recorders.
My thoughts on the following (sound quality only)
Marantz PMD661: Excellent sound quality, preamps are great unless you go to max, but with my very low sensitivity MD46, a level of 7 out of 10 was sufficient to provide excellent -12db audio.
Roland R26: Decent preamps, better sound, some noticeable hiss.
Zoom H4N: Bad preamps, excessive hiss, however nice sound quality at lower levels.
Tascam DR100 Mk II: Almost same level as Zoom, slightly better preamps.
Juicedlink CX231: I was unable to reach -12db on the camera with the gain set to high and the trim knob cranked all the way with my MD46 Dynamic mic. I normalized to -12 and experieced the same amount of hiss as on the Tascam recorder.
Thoughts on the devices (hardware)
Marantz: Nice build, locking XLR jacks. Old school operating system is a bit of a put off though for the money.
Zoom: Have used it for years, excellent build, lacks locking XLR jacks.
Tascam: Includes locking XLR jacks, very plasticy build.
Roland: Horrible handling noise, you cannot touch it at all while using internal mics, works fine with plug in mics. No locking XLR jacks, nice screen, decent o/s.
Juicedlink: It's a metal box with switches and knobs, no complaints.