choice of antennas

[VK4TJF]

which one will be the best compromised antenna for dx
a monoband gap antenna for 40 meters
or a 40 meter dipole up at 20 feet off the ground

[WX7G]

The monoband Gap will be better for DX. If the dipole was up 40 feet or higher it would be the winner for contacts broadside. 

[WA8UEG]

I hate verticals but with the choice given the vertical will do a better job then a dipole at 20'.

[W1JKA]

     Try a 40m dipole at 20 ft. first,if you are not happy then go the vertical route.Don't get all hung up on height numbers.My two 40/20 m qrp dipole dx antennas started out at 42 ft.and ended up being most effecient at 23 ft.Bottom line, antenna effeciency all depends on your own particular qth and GROUND conditions. Experiment first.

[W8GP]

This is a very common question,there have been many recent threads dealing with this very subject. Do a search for 40m DX antenna, vertical vs. dipole, etc. and you will find the information you are looking for.

[KB5UBI]

Install both. They both will have advantages. A Gap would not be my 1st choice and a radial field is a necessity, not an option.

[WD4ELG]

Speaking from my own experiences, I agree 100% with KB5UBI.  You can never have too many antennas for different scenarios.

[NK7Z]

which one will be the best compromised antenna for dx
a monoband gap antenna for 40 meters
or a 40 meter dipole up at 20 feet off the ground

The GAP will by far beat the dipole...  I have a review of the GAP Challenger as compared to a dipole at about 25 feet at my web site below...

[N0NCO]

which one will be the best compromised antenna for dx
a monoband gap antenna for 40 meters
or a 40 meter dipole up at 20 feet off the ground

A 40m dipole at 20' AGL is essentially an NVIS antenna, or 'cloud-burner'. Most of its signal will be directed upward, rather than outward. As others have noted - even an inefficient vertical will likely outperform a 20' AGL 40m dipole at the low launch angles that are typically required for long-haul DX.