T39 by a mile.
I keep my old T39 for when I go to places like Brazil where reception is
poor - neither my T68i or the T610 will get a signal in many areas the T39
will.

I suppose the T39 should be better by definition but I don't really know if
it is any better regarding reception. I personally prefer external antennas
and flips on the phone. Regretfully the T39 was probably the last model ever
to have an external antenna and a flip.

I just upgraded from T39m to a T68i and my wife has taken over the
T39m. All I can say is that I could not practically tell the difference
in RF reception between the two. I am talking about the same carrier,
same pattern of usage and identical locations. And supposedly T610 is
"better" than T68i in that department. Both T39m and T68i lose their
reception at the same corner in the my house. And every friend's Nokia
also suffers a similar fate at the same location.