My job requires me to be on my feet between 12 and 16 hours per day, 5 or 6 days each week.  Dansko clogs have been a saving grace for much of my 15 year career, and are the only reason I am still able to work such long days. They absorb much of the shock from walking on hard surfaces, they accommodate swollen feet, they improve my posture - which alleviates a lot of back pain -, and the extra thickness of the sole keeps my feet warm and dry whilst walking in snow and on cold surfaces.  I've owned five pairs of Dansko clogs over the last 10 years, and I have worn all of them until the insides were shredded and/or the toes were worn through.
When it came time to replace my most recent pair, out of sheer curiosity and frugality I decided to compare Dansko to Sanita. I ordered 1 pair of Cabrio leather clogs and 1 pair of Patent Leather clogs from each company.  The Dansko were the new XP, which purport to have memory foam inserts.
A number of years ago, I started ordering my clogs one size bigger than my normal shoes. I'm not sure why clogs fit this way for me, but I get better support for my instep with the larger size.  Moreover, my first couple of pairs of clogs were so stretched out after a couple of months of "breaking in", that they no longer looked professionally appropriate to wear with my uniform.  A lot of people complain that the toe box on both the Dansko and Sanita clogs is narrow.  I find that the toe box is sufficiently roomy if I order the next size up.  If it makes a difference, my normal size is an 8 1/2medium, but I wear a 40medium (9.5-10m) in both Dansko and Sanita clogs.  Since I began wearing the size 40 clogs, the toe box holds its shape and the leather doesn't crack as much on the sides.  Furthermore, I feel like my feet are better supported, and I really don't feel any additional slippage.  Additionally, the heels of my socks last longer.  I've now owned 3 pairs of Dansko clogs in the larger size, and thus learned that these clogs DON'T NEED BREAKING IN.  In my experience, if one must "break them in", one probably needs a bigger size. This is especially important to consider if one purchases patent leather, as the plasticized leather doesn't 'give' enough to really accommodate much stretching.
Now for the comparison: there is no remarkable difference between the two brands - EXCEPT FOR THE PRICE.  Each leather type looks very similar to its counterpart from the competing brand.  The Dansko XP "memory foam" insert doesn't feel any more cushiony than the Sanita insert; however, the "memory foam" insert does seem to take up a little more space than the Sanita insert, making the Dansko feel a little, tiny bit tighter.  Also the Dansko XP insert is a lovely, soft leather, which is not personally preferable due to its tendency to break down from the continuous friction of the foot moving around in the shoe. The Sanita insole is soft yet durable. The soles - or "platforms" - look similar and feel the same underfoot.  The staples are the same quality, as are the no-slip treads.  Neither shoe has better "workmanship" than the other, nor does one "squeak" more or "feel heavier".  They seem to be relatively the same shoes except that the Sanitas were 2/3 the price of the Dansko.
If you've never worn Dansko or Sanita clogs, or even if you've only worn Dansko, do yourself a favor and buy multiple pairs and do a fit/appearance comparison for yourself.  Both Amazon and Zappos offer free shipping/returns on most shoes.  Or, better yet, go get properly sized at a department store which carries the clogs.  Many of my co-workers were able to be properly fitted for Danskos at Nordstrom.  It is now my experience that if one wears a particular size in Dansko, one would likely wear the same size in Sanitas.
I'm keeping the Sanita clogs for the singular reason that they cost less.