I did know I shouldn't have posted my questions to the "alt.hvac" group, so
below is the SAME post I had there on that group. I cut and pasted it
here...sorry about that....this the full story:

Is this a newsgroup where a homeowner can ask a recommendation on a
furnace/AC and on Duct cleaning (is it a scam)? My head is spinning after I
had 5 estimates done (2 from big companies, 3 from small, local ones) and
they were all so different and contradicting in what they advised that I'm
left very confused with what is right. I'm down to two guys who own small
local businesses.

One gave us a quote on a Rheem Weather King 80% and 2.5 ton AC and told us
to stay away from the variable speed, the other gave us a quote on a Carrier
Weathermaker 58CVA 80% variable speed furnace and a 3 ton AC (Weathermaker
38TKB). From what I was told, an air cleaner comes with the Carrier 58CVA
and we'd have to buy the media air cleaner extra with the Rheem, which is
not a big deal, we'd buy that. The difference between the Rheem quote and
the Carrier is about $1400 more for the Carrier when all is said and done,
but I think the Carrier guy is doing a little more work.

Here are some things that might make a difference, I don't know....The
Carrier guy mentioned we'd need to put in cold air returns higher on the
walls upstairs (the ones we have on the second floor are near the ground)
and he told us duct cleaning is not worth the money, when we asked about
having that done. Feels that's a bit of a scam and the ducts will get as
cleaned as they need to be when they do this installation and position the
furnace, etc. The Rheem guy didn't mention those things.

Is duct cleaning a scam? I have no idea and am about to drop an additional
$400 on that if I go with any one of the other guys the Carrier one who
thinks it is a scam.

Do we need air returns higher on the walls upstairs on the second story to
make AC more effective?

Both guys seem to know their business, both come recommended by friends and
have no bad reports with the BBB....and I have little else to know what to
base this all on. Both have been in business for many years and I think
will stand behind their work and are personally involved in the installation
of the units. How do I go about picking? Which equipment is better?