I've found the cheap, single-conversion, park flyer receiver to be good only if you aren't flying around other TXs in the same band (i.e. flying by youself at a park). At my club, I got some bad glitching when flying in front of the flight line (near other TXs). Because of this I pretty much stick to dual-conversion FM (PPM) RXs, even in my park flyers. However, I do have a couple PCM receivers for my helis, and recently got a few 2.4GHz spread spectrum receivers.

Note that there is a difference between the "cheap park flyer" RXs I spoke of, which have limited range, and full range single-conversion RXs (most or all of JR's RXs are single-conversion, and Futaba, Berg, and Hitec make some full range single conversion RXs, I believe). I have no personal experience with these full range single-conversion RX's, but I'd expect them to be on par with the dual conversion receivers.