RADAR is the ultimate (IMHO) when it comes to quality ADA converters, etc. I know a guy who uses his RADAR, and then transfers his stuff to Logic for editing. The sound is unbelievable!!
I hear people talk a lot about the quality of the Alesis HD24xr converters, too - although there are just as many people who say the HD24 is just "ok"
The reason people would choose a stand-alone (IMHO) - the reason there is still some market share in that area - is (typically) the ADA quality is better & because the system is rock solid. I have spoke to people who have not had (1) crash or lockup in the middle of a session, or just foolin' around, in their 10+ years of using - but again, I am speaking of the RADAR system. Their argument is "how many [DAW of choice] users do you know who can say they are in the same neighborhood with stability?"
Just my 2¢.