If I had to choose, I'd always choose a half-wave 80m vertical in
preference to a half-wave dipole.

In general, I'd prefer the dipole on 80m. But I work mostly
close in within say 600 miles on average. A dipole will smoke
most verticals at those short distances. If the dipole is at least
30-40 ft off the ground, it will still be capable of dx.
If I worked all dx on 80, I'd rather have the vertical, but being I
don't,
I prefer the dipole.
Each band is different, and it always depends on what path/distance
etc, I want to work as far as the preferred antenna.
In general, I'd prefer the vertical on 160m.
Dipole for 80 and 40, and usually 20.
I've tried both a 1/4 GP and a dipole on 20m for average use,
and found I prefer the dipole. Probably ditto for 17,15.
But on 10m, I prefer a 1/2, 5/8 vertical if I can't have a beam.
On 10m, you see quite a bit of local chatter, and most tend
to run vertical if they want a decent ground/space wave.
It also gives them a good dx signal. If you run a dipole on 10m,
your long haul will be good, but local operation fairly poor.
There really is no best type antenna except to suit the job at
hand. If I'm on 40m in the day, give me me a good dipole,
loop, etc . But 40m at night 800-1000 miles to the coasts?
I'd rather be sitting in my truck running the mobile. No joke.
It will do a better job vs my appx 40 ft tall dipole. That
was tested over and over again. No fluke of the band cdx.
On 40 at night, which is best will nearly always be distance
determined. Look at the lowly efficiency of the mobile vs
the dipole. At night, it doesn't really mean squat. What matters
is that you have radiation at the angle you need to make that
hop. My mobile spits more rf at the desired angle than my
40 ft high dipole does at those semi low angles despite being
half crippled as far as efficiency vs a full size antenna.
So polarization is nothing to ignore if you want the best
bang for the buck. I bet my mobile ant sitting sideways would
be pretty lame in that case. Or say take two like mobile antennas
and make a short dipole. It would stink up the place on those
long hauls vs the normal vertical mobile antenna. But it might be
slightly better in the day working 200 miles away.
The best is to have both. And use a switch to be able to
quickly compare. You will see some interesting things as
far as band cdx, signal fluctuations, etc over time.
It really boils down to using experience working the various bands,
at the various times of day, season, to know which will likely
be the best at a given time. It's 1.49 in the AM here right now.
If I had to get on 40m right now, give me the vertical any day.
That would change in a few hours though when I started losing the
long haul stuff and had it replaced by the various old farts and
rednecks I work on a more local scale. :/ I'd then be on the dipole.
MK