Of course Yagi beams or quads are the best solution for the DXer. Unfortunately I cannot erect a tower so I had to look for other designs which could fit between cooperative trees. The lazy H is really a great antenna. I use 2 of them, one beaming towards NW and SE and the other one towards NE and SW. They are fed by an automatic  symmetric tuner by Klaus Bemmerer http://www.hamware.de

Stacking dipoles is a well known solution used in short wave broadcast. This is a picture  of the swiss national broadcast antenna which was unfortunately torn down in 2005 (short wave broadcast seems to be disapearing everywhere except in the 7100 to 7200 kHZ segment).

Most of us don't have the possibility to stack more than 2 dipoles and this antenna is called a Lazy H. Gain is not the only interesting aspect of this type of antenna. Very singular and useful is it's faculty to maintain a Mexican hat like vertical profile over a wide frequency range while the multiband dipole tends to radiate more and more energy towards the vertical as the frequency increases.

The horizontal radiation pattern remains similar to that of a dipole too, without multiple lobes. The main lobe keeps a constant orientation on the whole range.

Gain realised when stacking dipoles (source  H. Jasik, Antenna Engineering Handbook). Take notice that the gain can be over 3 dBi with only 2 dipoles and that it shows intersting values over a wide range of spacing, typically for wavelengths between 20 and 10 meters.

Gain that can be achieved with a lazy H compared to a 1/2 lambda dipole at 1/2 lambda height

This is what happens when you tune a perfect 1/2 lambda 20 m dipole at 10 m height on 21 MHz.... noise when receiving and cloud warming when transmitting

Mulztiband lazy H's must be fed in the centre of the phasing section.

Good overall results on 14 to 28 MHz when H=8 m, lower dipole at 9 m over ground and dipoles of 13 m overall length.

This antenna can be used on 30 m too.