Regarding just base antennas, in my experience, Diamond and Comet are pretty much interchangeable. They are both colinear designs with matching sections between the internal elements. They both have fairly thin fiberglass radomes that flex in the wind and shatter when hit by lightning. They both have joints so that they can be broken down into ship-able lengths. Diamond uses metal fittings at the joints that screw together. Comet uses plastic joints. They are both prone to flexing with the resultant water leakage where the radome meets the base. The really long ones, like the Diamond X500 and X700 really need to be supported about 2/3 of the way up to hold down the flexing. The shorter ones like the X30 and X50 work just fine. They aren't made in China--they are made in Japan, though there are Chinese rip-offs on the market. Some of the rip-offs go by somewhat recognizable names like Browning and Tram. Some of the rip-offs actually reproduce the Diamond or Comet logos.
