I have and enjoyed the N770, N800 and now the N810 and all are great. As you did not state what your needs are it is hard to say which is the wiser one for you. If you are tight on $ and only wish the basic (yet great) video/music/learn about the "IT" then the N770, if you also want the best all around (w/o the HE version on the N770 - e.g. skype/etc) then the "bang for the buck" wiser move would be the N800, however, the N810 is "cool" and while I find the GPS a major disappointment, yet all else a great step forward. So, if it was me - IF $ - is the top filter I would go for the N800. whichever you get they all are outstanding.

As a side note, I spent hundred of hours to get the N770 to equal the N800, and as my N82's GPS (running TomTom) is outstanding I have not spent much time on working on the N800/N810 GPS. Mostly due to it not working very well on the 7 day trial - if they gave 30 days I might have been able to get a better feel for it. Even if I was to work on getting the N800/N810 to work on Maemo Maps like the TomTom, I would STAY AWAY from Nokia's software both due to my feeling it is a ripped-off solution ($150 for lease vs $150 forever - a 3 yr auto lease is about 1/10th the cost of the auto bring the Nokia's worth $15 or tops $25 not $150) and found it poor in function compared to the easy of TomTom.

Cheers,