Many people would like to have a single multiband wire antenna covering as many bands as possible.  The antennas considered here are:

• A Resonant Dipole fed with Balanced-Feedline (Doublet).
• An Off-Center-Fed Dipole (OCFD).
• A G5RV or its improved version, the ZS6BKW antenna.
• An End-Fed Halfwave Dipole (EFHW).

THIS Page focuses on the first two (OCFD vs. Doublet).

The Doublet and OCFD are fundamentally the same size and are both quite good multi-band antennas, but the Doublet requires an antenna tuner on all bands, whereas the OCFD works on most bands without a tuner, requiring a tuner only on a couple of bands.

I often hear people recommending feeding an OCFD antenna with 300 Ohm twinlead, based on the (false) assumption that the feedpoint impedance of the OCFD is about 200 Ohms on all bands.

The problem with that is, these people are only focusing on the theoretical Impedance/SWR, while ignoring the main drawback of the OCFD, its strong tendency to generate heavy Common Mode Current.

When Common Mode Current gets onto the feedline, the feedline itself becomes part of the antenna, which not only radiates, it also changes the resonant frequency of the antenna. 

How much the resonant frequency changes depends on the length of the feedline.  It often results in losing low SWR on one or more bands.

In order for an OCFD antenna to work properly, it requires sufficient choking directly at the feedpoint to prevent CM Current from getting onto the feedline. 

A good value of Common Mode Impedance (CMI) to shoot for is 6k Ohm.  8k Ohm is better, allowing extra CMI for cases where the antenna is erected in a less than perfect installation. (Example: feedline coming diagonally away from the feedpoint.)