Good choices of phones.  I had a 6230 (not i) when it came out and it
worked very well.  The menus are very fast and it also played FM and
MP3's.  The downside is that the memory requires that you shut off the
phone and take the battery out to access it.  It didn't include a usb
cable to connect to the computer and bluetooth is really slow in
transferring data.  Needless to say, I don't update my songs on the
memory card that often.  I think that the maximum memory listed in it's
manual is 128 but I've had a 256 and it worked fine.  It's a phone
who's stronger personality is more of a phone than a MP3 player.  After
Sony Ericsson came out with the w800i, I waited and waited and broke
down and bought one.  One nice function I liked is that you can leave
the phone function off when you turn it on and use it as a MP3 player
walkman only.  This is really nice with using it on the airplane or the
hospital where cell phones are required to be turned off.  One bug that
I had though was the program Disc2Phone used to transfer the MP3 files
have some real issues.  After finding out other people's solution to
it, I got a usb card reader and it has been great since that discovery.
What also nice is that you can take the Pro Duo card out as the phone
is on.  So it's been really easy to update the music I want.  I just
used iTunes to manage the songs and drag and drop from iTunes to a
windows explorer window opened to the memory's MP3 folder.  The phone
also comes with a usb cable which is nice but as I mentioned, you can
only do so much with transferring music until the bug is fixed.  The
w800i functions well as a MP3 player and a phone.  But I have to admit
that the menus in the Nokia was faster and there are more 'shortcuts'
functions with the Nokia but Sony has put some thought into it as well.
As you can see it's not a definite answer but I'd go with the Sony
even though I've always been a loyal Nokia fan.