SACD

Generally, you are right.  In most cases, an SACD will give you a more realistic soundstage and better instrumental timbres.  This is especially true if the SACD was made from a very good analog or DSD master.

Unfortunately, there are some SACDs which were made from CD-format masters, and you can't make a silk purse from a sow's ear.

And there are some Redbook CDs (like most of JVC's XRCDs) which were recorded and produced with such great care that they rival SACD in sound quality (though IMHO imaging is never as 3D as an SACD).

All things being equal, the quality of the recording (and physical production of the disc) make huge differences.

The last factor is the playback device.  The first time I heard an SACD, it was on the Sony SCD-1 ($5k) and it was glorious.  The next time was on a $250 Sony 'universal player' and I was not impressed.

I personally would not buy a player that doesn't handle SACDs or a DAC that cannot decode DSD64 and probably DSD128 (double DSD). 

@Elizabeth , I'm really sorry that you haven't heard how good SACD can sound.  I'm really perplexed when you say that SACDs lack air and ambience.  I've found just the opposite, that a well mastered SACD gives me room ambience that even the best CDs cannot match.

I'm not questioning your ears, but there's got to be something 'wrong' for you to hear less 'air' on SACD than Redbook CD.  Not trying to argue, but I bet that one day you will hear this yourself. (When you do, remember me ;-)

Oh, and I'm definitely talking 2-channel... and even mono.

Happy Listening!