First of all, your expectations are probably too high for CRKs also. They are great, but they will not likely result in pyrotechnical display emanating from your backside.
If you expect a very well made folding knife that cuts no better than a knife 1/5th the price, then order one up. Seriously, I think these things are fantastic and I love mine a lot, but I see too many guys buying them expecting a huge wow factor after trying a 100 dollar benchmade or spyderco, and honestly, it takes quite a bit to sense the differences between a nice production knife and a CRK.
That said, I would recommend the 21 first. I did the Umnumzaan first and got one of the earliest models (highly desirable now), and I was coming off a production knife buying spree and wanted the WOW that I read about. I was underwhelmed. Yeah the knife was a bit smoother than the Spydercos I bought, but it worked no better in use. Simply put for a knife I was using blindly, it was not worth 4X the price to me at the time...so I gave it away.
Now, I feel a bit differently. I like the feeling of holding, fondling and using a knife that has subtle hints of a man's life passion. I like knowing that a design team did not work on this knife for 6 months prior to putting it into production, rather a man built knives by hand for many years and evolved a design over 21 years to arrive at the refined version I hold in my hand...and yes, I enjoy the (slight) exclusivity that the knife has. I even enjoy the idea that 99% of the world can not possibly understand how I can see the value in this knife.
Think of it like the difference between a 20 dollar cigar and a 100 dollar cigar, or a 50 dollar bottle of wine, and a 500 dollar bottle, or sipping a beer from a frosty mug vs drinking it from the can. There are subtle differences, and the returns are arguably highly diminishing, but if you take the time to understand the differences, it might be worth more that the price to you...or not.
Do any of these examples strike a chord? You can get coffee in a lot of places, can you contemplate how a hand pulled espresso is preferable to some over a cup of Joe from the nearest quick shop? A lot of people cannot.
I say the 21 because I believe it is the prototypical CRK with the bushing system, and it is available in the most options. I think a person should look at them all and pounce on the one that speaks to him/her. limiting your search to what is in stock, or what you can afford at the moment might be limiting your experience.
I do not expect the 21 to be going anywhere anytime soon....but who knows.