All these observations are anecdotal and may not point out small differences. There is an excellent review of small shortwave radios, including the ATS-909, in the August 1997 issue of QST . The consensus on rec.radio.shortwave seems to be that the 390 is not a particularly sensitive radio. The Yacht Boy is said to have better sound, but performance is similiar. The 7600 does have synchronous detection, but lacks some amenities on the 909, such as a signal strength meter.
Reviews are mixed on rec.radio.shortwave .
One camp proclaims the 2010 as superior, mostly due to its synchronous detector that the 909 lacks. Mediumwave performance of the '909 is decent, typical of most SW portables. However, like most portables, it can't compare to the Superadio, unaided , due to its much smaller mediumwave loopstick. I'm not much of an FM listener, but I do prefer the 909's digital display to the horribly inaccurate analog dial on my Superadio. There is no date function, therefore the radio is Y2K compliant by default.