I would like your opinion on what you regard as a 'top of the line' handheld scanning receiver.
Heh, nobody has built one yet to MY specifications.
Thing is, the most expensive scanner in the world isn't going to go as far as the guy with the $99 special, but is backed up by experience and knows the limitations of his gear. Much of that I got right here over the years - so thanks to the RR users!
How do you rate the ICOM IC-R20?
Definitely a receiver first, with some scanning capability. Obviously analog only with no trunking, and for some it takes a bit getting used to the programming. Dual-watch is handy and preferable to "priority" scanning sometimes. HF is good and stable, and can be very fine-tuned. But for extensive HF usage, you'll be wearing out the keypad and/or knob quickly, so that can become tiresome. Of course it benefits from a real antenna, although unlike most other receivers, you have BOTH RF-Gain, and overall Attenuation at your disposal in case of overload. For HF use, like the R5/R6, I feel it is a niche product. If you have to have HF in your hand, the R20 does well.
It really is all a balancing act of trying to decide what compromises one is willing to make for extremely broad coverage, and overall usability in a small package.
If you are into airband coverage, either VHF or UHF milair it does great if you like to sit on a specific freq. However, if you are scanning a large amount of set frequencies, you can easily miss transmissions. I would actually recommend something a LOT faster than the R20, even if it doesn't have the same good receiver specs, to be able to nab those quick transmissions. Of course there is a middle ground of scan speed that one would have to decide upon for themselves. I sit on freqs with the R20 or R6, but use a much faster scanner for actually scanning.
So even if you don't intend to use say a digital or trunking scanner, if it has the speed and band coverage you need, you can ignore what you don't want to use - it might be a better overall choice than the R20.