Being one who has a similar site, I would have thought who.is or whois.com were the most accurate. Mine is different in that I capture the information at the time of an attack, spam, or other similar event. However, most other sites will re-query the whois data when the page is accessed assuming that there is a measure to ensure that the same whois data is not being requested to often. Some sites subscribe and download bulk whois data from time to time and update their databases that way instead of relying on traffic. With a large site such as these, it is nearly impossible to keep the data 100% fresh. There are limits to whois look-ups and sites have to be careful not to over do it.
The best thing to do is either use
nslookup in a Windows command window or
whois in a terminal window in Linux. This will give you the current whois information. But be sure not to try and make bulk queries or you just may be blacklisted. Spread them out a bit and you should be fine.