I am not sure that one is more "desirable" than the other. It really comes down to what you want out of the gun. The 6906 will be lighter, more compact, and easier to carry. The 5906 will be heavy, large, and have a slight edge at the range in terms of accuracy. Frankly, both guns are very good, and it is tough to go wrong with either choice.
I carried a 6906 as a duty gun and loved it. I never had a FTF or an issue. It will shoot as well as 99% of the people shooting it can. It's small enough for CCW as well. I have my wife carrying one, that says it all. I will warn you, buy one and you will soon have 3. They are addictive. I've found them for as little as $275 on the web, there is nothing even close to that gun for that amount of money anywhere.
The only issue I would have with the 6906 for concealed carry is the double stack design would be wider than say the single stack 3913. Still would be a viable gun for CCW.
The beautiful thing about the 3rd Gen's is that none of them are a bad choice.
Just that the OP was talking about those 2. A different question would have been to help him choose a CCW. I am ASSuming that he has temporary access to those 2 models and he better act before they are both gone.
I bought one of each from CDNN when they were selling them out new. Then I saw their first sale of police trade ins and bought another pair. The second pair were damn near as new as the first! Both models are great shooters. I am even toying with the idea (heresy!) of replacing my BHP with one of them for work. I got some of the mag adapters that allow the 59 series mags to be used easily in the 69 series, and I think I have found the replacement 9mm. Switch to the shorter 69 mag and am ready to go off duty or PC. I cannot get much difference in accuracy between the 4 guns. In fact the most accurate (by a hair) is the used 6906.
Like all 3rd gen S&W semi autos you will die of old age before you wear one of them out. Both guns are getting to the "If I could have only one handgun" list..................
I have 2 5946 (DAO 5906 without the safety) love em! But I'm new to these type of guns. Always just had polymer ones. So far two 5946 and one 1006 and while that's it so far I'll defiantly be adding more!
If you get both, you'll have the beginning of a nice collection of great pistols. The carry question is the only point that would make one a better choice (6906).
I carried a 669/6906 on duty for about 13 years until we transitioned to the .40 cal. Sig P226R. I recently bought a 6904, the blued version, because I miss the old Third Gen. I'm kinda pissed I got rid of all my old holsters, but I did have plenty of hi-cap mags left over.
I trucked the 6904 out to the range at SWAT training one day last year and cleaned a course of fire with what the kids saw as a "relic." It was like driving your first car again...
Was looking for a like new 5906 when I found a 6906 in that condition. Bought the 6906 and like the gun. Smaller and lighter than the 5906. So far no malfunctions with any ammo I have tried.
I had a 5906 that was basically new and loved it until I purchased a 3913 and 6906. Both compact pistols shot as well as the large 5906, so I traded the 5906 off.
The 6906 is a great all around gun. Just big enough to be a fun range gun, yet small enough to CCW. 13 rounds of modern 9MM defensive ammo is pretty good in a package like the 6906.
If I want to shoot a BIG 9MM I go for the CZ-75 or Browning High Power, a couple of outstanding full size service pistols.