No, most of them are terrible and I wonder how they even exist!
In my area, my local MLS owns a public access MLS site that is by far the best I've seen. Most sites are inaccurate, out of date and limited on the information they provide. The benefit of visiting a site that is owned & operated by the local association is that the information is the most accurate and comprehensive as well as the fact that it is the most current. Many sites pull information from other sources (such as mls's and Realtors websites) and much of the information gets lost or garbled in translation (for instance, I had a rental that repedatedly got listed as being for sale - at the monthly rental price. I never posted on that particular website, the pulled it from another site).
Hope that helps & good luck!