I am looking for a portable audio recorder to shoot separate-system uncompressed audio with a 16mm film camera. In the past, I have used a Sennheiser cardioid mic and the Marantz PMD660. It seems that the PMD661 has everything I liked about the PMD660 but with notable improvements: it's more compact and sturdy, it has a very clearly legible screen with user-friendly navigation, SD storage instead of CF, improved pre-amps, 1/8 inch headphone jack, RCA outputs.
My question is: what advantages might the PMD671 offer over the PMD661? The 671, though marketed as Marantz's top-of-the-line professional solid state recorder, seems more bulky, it's screen seems harder to read, and its controls appear more complicated. The only substantial difference I can see is that it has a limiter--does this alone account for it costing much more than the 661? Would a limiter be an absolute necessity for less predictable, documentary-style recording?
The PMD671 also has a digital output. The form factor of the 671 is more desirable for some people for field bag use. It has the big red record switch on the top panel, which can be useful in the field. But these differences don't really justify the difference in price.
A limiter is certainly a good thing to have in a piece of gear, especially if you can turn it off when you don't want it, and adjust it to your liking. The difference in price between these two units is more of a legacy thing. The 661 is a much newer design. Back in 2004 - 2005, Marantz was one of the only manufacturers that made solid state digital field recorders. All of the small handheld digital recorders that we know today (Zoom H2, Edirol R-09) had yet to come out. People wanted them, they just didn't exist yet.
The reason the 671 is more expensive is because at that time, there was a very similar recorder out called the PMD670. The 670 had a limitation. It could only record in 16-bit, with the highest sampling frequency of 48 kHz. The 671 came out next and offered 24-bit 96 kHz recording. Likewise, it was also a bit more expensive.
As to which machine is better, I can't say. I haven't used the 661. If you used a Marantz before and liked it, then I bet either one of these would be fine. There are lots of good digital recorders out now.