...been awhile since I posted my OP

I finally proceeded with a trial, albeit anything but scientific.

I bought Behr primer, at 11.99/can, SW Drywall primer at 21.99 (or
maybe it was 19.99)/can, and PPG Speed Hide primer at 19.99 less 10%
discount (17.99/can), Kilz general purpose primer at 11-something a
can. All cans are 1 gal buckets.

I used them mostly on unprimed drywall. I also used them on some bare
pine. I used a Purdy brush and Shur-Line rollers. The surface temp
was 50-60. The dry-time temp was 60-65. I'm painting a 24x12x8h room
(office) in my detached garage/shop. I'm also painting the rest
(24x24x8h) when temps warm. I did lay down some Kilz in the corners
and about 12 foot of one wall.

I did not use the SW on a large area of drywall. It was the last one
used, and the drywall I have remaining is too cold to prime at this
time. I only used it on some bare pine window trim.

Here is my random thoughts and perceptions..

Behr is the white-est and thinest. The tape and mud work are very
visible once it dries (and during application). It went on well with
a brush. The Kilz took a bit more effort to apply with the brush.
PPG is the least white but clearly thickest -- it nearly hides out the
tape and mud work. It applies well with a brush -- a bit less effort
than the Kilz, and again, much thicker than the Behr.
Kilz is somewhere between Behr and PPG, but seems to leave a slightly
better finish than Behr.
I topcoated with some 2-4 year-old Behr Prem Plus mid-tone green
paint. On the Behr primed wall, the sheen seems a bit glossier than
the PPG primed wall. The difference on the Kilz primed wall is
negligible.
The PPG maybe gives a slightly more uniform and consistent look and
feel -- this is highy subjective however.
The topcoat will need a 2nd coat -- or at least some roller touchup to
cover well.
The SW is thinner than the PPG, a bit thicker than Behr.
The SW has a very unique and distinctive odor.
The Behr has an amonia odor.

I cannot really pick a clear winner. If I was tempted to chose one
for a single coat coverage -- say for my ceiling and it would not be
topcoated, I would clearly chose PPG. It just about hides the tape
seems. I'm not sure if the PPG should even be used for a one-coat
however. If not, then this point is mute. But, I do plan to buy
another gallon of PPG and finish my ceiling with it -- and possibly
just call the ceiling done. I do not find any points about topcoating
on the PPG container. On the SW it clearly states it should be
topcoated. Once a topcoat - even just one coat is applied, it's hard
to find any real differences. This pretty much leads me to the
conclusion, that the primer may as well just be of the same brand as
the topcoat and forget about all other factors. The primer, assuming
there is some design behind it, is probably most effective with a
paint from the same company. It also sort of leads me to seriously
consider that for existing paint, the better choice may be one from
the same company. In otherwords -- if my house is painted with BM on
the exterior, maybe it's best to use BM again for future painting.
For interior I would not worry about it.

Looking at this differently -- I don't see a strong correlation
between price and final result. While I've yet to give the SW a fair
shot, it's going to be really hard to justify $20/gal when the Behr/
Kilz are $12/gal, and the PPG at $18/gal clearly does hide much
better. If I needed the hide, the PPG wins, but on a topcoat or two-
topcoat scenario, then the less costly Behr/Kilz options seem pretty
reasonable. If I had easy access to Kilz paint, then maybe I'd opt
for the Kilz primer. If the WalMart brand paint is really Kilz, then
I guess I do, otherwise, Behr, Valspar, PPG, SW are more widely
available to me.

For the average DIY-er, I cannot overwhelmingly see paying 2x for SW
or even PPG. Maybe if I was doing this daily or even monthly, I
could find a better agrument for a more expensive paint. As it is --
when painting once or twice a year, the bigger issues tend to be
moving around furniture, prep, and the struggles with cutting-in, or
taping off. To that end I picked up a $3 Shur-Line pad with 2
rollers that claims to be good for trim. My initial impression is
that it shows promise. Cutting-in with a brush along door/window trim
is never crisp enough for me. I get better each time, but it's a
painstaking job and when I do this only once a year, it takes me hours
to re-learn.

This is clearly not addressing the longevity of the primer or paint
job. But then again, for interior, I'm not convinced it's going to
make any difference. I'd just buy the top line of paint from
whichever brand I chose. I'd used a gloss or semi-gloss on trim
(personally I like real wood anyway) -- and flat or eggshell. My
guess is that after 5 years the paint will look very good and that in
10 years it will still look good. And in 10-15 it's going to be
repainted anyway.

Sidenote -- the Behr topcoat paint really sticks to my brush. It was
a brand new Purdy and I cannot get the brush like-new clean after
scrubbing with soap and water for 30 minutes. I only painted about 2
hours max with the brush. Maybe that's a strong point for the paint,
but it really stinks that I cannot get my brush clean. For this issue
alone -- I could be swayed to another brand ;-)

So -- there ya have it. I'd love to see a 6 sided room - each
painted with specific brand (Behr, Valspar, SW, BM, PPG, Walmart) by
the same painter.