I've owned several AVRs, starting with my first low/mid-range one years ago, which featured Audyssey MultEQ, the most basic version of Audyssey that also calibrates the subwoofer. After that, I upgraded to an AVR featuring Audyssey XT, and more recently, XT32. I have always remembered my first Denon with MultEQ very fondly. The first time I experienced the calibration results while using Dynamic EQ, I was very impressed; everything just sounded great.
Then, I upgraded my system to one using XT, and while it sounded decent, I was never fully satisfied with it. I must have calibrated it 50 times, finding that XT tended to overemphasize the high frequencies too much. Sound quality was a bit tinny and harsh—acceptable, but not ideal.
From there, I moved to my most recent AVR, which features XT32. This was a definite improvement over XT, and I've been mostly happy with the sound quality. However, I couldn't shake the feeling that my first AVR sounded better to me. This thought lingered in the back of my mind for years, but I never bothered to actually do a direct comparison until today. So, I set up my old AVR, ran Audyssey with my current configuration, and lo and behold, the basic version of MultEQ indeed sounds better to me than both XT and XT32. Dialogue has much more depth, the high end isn't so exaggerated, and everything just sounds correct and tight. This made me think of an old saying: "less is more."
I believe there's something to be said about the simplicity of MultEQ in comparison to the other versions. It's a simple algorithm that isn't trying to do too much, which I believe allows it to be much more consistent. While it doesn't work miracles, it just seems to do a solid dependable job regardless of the room it's working with. On the other hand, XT and XT32 try to do much more, which means there's a lot more that can go wrong.
Reading through the Audyssey thread on AVS, I've noticed quite a few people claiming that MultEQ is indeed better than XT, mainly because XT tends to excessively tinker with the high frequencies. However, I think I might be the only person who believes it's even better than XT32. I know this will be an unpopular opinion, but it is based on my experience using Audyssey alone, without any further tweaking post-calibration, outside of the basics like adjusting crossovers and levels. If you read through the forums, you'll find many complaints about the end result calibrations with XT and XT32, but you won't come across any complaints about MultEQ end results- I looked and it's always mentioned fondly. I think it's Audyssey's most dependable algorithm!