I had an Achros 605 and a Nokia N810. I would say that as an end user, the N810 was much better.
First of all Archos mislead me into thinking all I had to do for my 605 was just download a plugin to play h.264 movies. However, it turned out, you had to actually pay for that plug-in (yeah, I should have done the research, but I didn't think they would charge me so much). Also, I managed to crash the 605 easily by skipping through songs "too many times". It really sucks to have your whole MP3/MP4 device reboot on you just because you wanted to skip to the good part of a song. I know this article is about the Archos 5 and 7, but my experience with the 605 is bad enough that I am right now recommending people to not trust Archos.
The N810 is so far much better. I can still find a few bugs here and there but nothing so far that can completely crash the whole system (even when using "unsupported applications"). The fact that they encouraged open development on day 1 has allowed a huge 3rd party library of applications since the day I got my N810. On top of that, they give me a simple terminal shell so I can run console applications without have to do crazy GTK or Qt porting.
tl;dr: The N810 is a better system for end users anyway.