A test comparing my home and car antennas on 14MHz using WSPR
At home, I used 5 watts into an end fed wire that was run along the gutter, with the feed point just inside the upstairs window. This isn't cut to any specific length except to fit along the front of the house and isn't much more than about 7 metres long.
In the car I used a Watson Multi Ranger 9 band whip on a small Sirio mag mount. The mag mount should really be bigger for the HF bands (except 28MHz - this type of mag mount was also sold with a Sirio CB antenna). The transmitter was a SOTA Beams WSPRLite, with 200mW output.
The car was parked on the road outside my house.
Both the wire and the car are on the north side of the house, with the axis of the wire about 20/290 degrees. To the north there is a field across the road, then more houses around 100 metres away.
During the test, both transmitters activated simulatneously 3 times in their random sequences. There was some spacing between the frequencies so they didn't overlap, around 50Hz.
From those results, it looks like the mobile antenna would be best for all directions in an open area.
There were some stations who I was received by only when using the wire antenna and 5 watts, including those in the USA and Canada. Without the extra power, none of these stations would have received me as there was much less than 14dB margin above the limit of WSPR reception. The 200mW to a mobile antenna has got to the USA quite a few times before.