I personally would use the HTPC to play the HD content if it's powerful enough. It's much easier to do that on the computer rather than the PS3 since you won't have to convert the files to a usable format for the HTPC.
As for quality, I don't think there'd be much of a difference so it the files are already in a format that the ps3 can play, then it's just a matter of you deciding which you prefer the controls/software on.
Just my $.02
As for quality, I don't think there'd be much of a difference so it the files are already in a format that the ps3 can play, then it's just a matter of you deciding which you prefer the controls/software on.
Just my $.02