Which omnidirectional base antenna will put out the least TV
and telephone interference in the neighborhood?

A resonant one, properly decoupled from the feedline.

Someone with an antenna analyzer can check this for you, you're not just
looking for low SWR, you're looking for little or no reactive component to
the impedance in that band.

As an extreme bad example, I saw a radio shack salesman explain to a
customer how he could use their discone antenna (the one without the top
element!) for CB.
That antenna is dramatically too small to be resonant on 11m, it would have
just been an efficient radiator for any VHF-UHF band harmonics and noise
that the rig might produce.



--
KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR