The Taurus 85 is the same size as the S&W but weighs around 21 oz, The S&W weighs around 15oz. The extra weight makes shooting +p's a little easier. It's a nice little gun for the price.
I own several Tuarus handguns, an 85,94,605,606 and a Millenium in 9mm. i've put thousands of rounds through them without a single problem. I have several more on my "gonna get" list.
Pretty much nothing, except the obvious factoid that the 642 is DAO.
The big difference between them and the Taurus is price, resale value, and (to a lesser extent) fit & finish and grip/accessory availability (although most J-frame holsters and speedloaders will work with the small-frame Taurii.)
I have a 642 and have owned 3 Taurus 85s.
One of the 85 was a SS CH model. I liked the trigger better than the Smiths, but the Taurus misfired fairly often. It took a year to go through the whole repair and return process several times and finally to get it replaced.
In any event, I would not buy another, and I like my 642, and also a 640 .357.