Puddin' Man wrote:

b.) Are lots bigger (condensing unit).

I replaced a 30 year old unit with 15ser Lennox last fall,
and as someone stated, it is taller, and fits on like a 2x2 pad instead
of the old 2x4 foot pad.

Any/all discussion of the old vs new stuff would be
much appreciated. "Los Federales" have made a hideous
mess of this kind of thing before, don't know why
they wouldn't again.

The new stuff in general is much improved, and more efficient. Generally
quieter as well. Consider also a new furnace. if that is part of your
setup.

And as always, a good installation is key, with someone who can service
the unit in the future.