There are 2 major things to consider when we're speaking about WHOIS:
1. WHOIS is a protocol (as mentioned before by
@Future Sensors) - it's not a tool, instead multiple tools (mentioned here as well) use this protocol.
2. There is
registry whois and
registrar whois data.
The registry whois contains all or partial data that a
registry has of a registrant, and the registrar whois contains all (or partial) data that a
registrar has of a registrant.
Some registries may not accept registrations of domains while using privacy services, however they will hide your information if you query their WHOIS (often '
REDACTED FOR PRIVACY') - this does not mean that the registry doesn't know the registrant details - they just don't display it publicly - possibly due to GDPR. Other registries however may display the full data, for example the registry that manages .US does display all data publicly and does not support whois privacy services.
Some registries (for example .ES) do not even allow direct querying of WHOIS via protocol, instead you have to do it through their website (nic.es).
Now, in regards to most tools mentioned here - the argument that they often show outdated data is due to the fact that they sporadically query all domain whois data - so the chances that the domain you're looking up whois for has already been queried for by that service are high (some offer a
Refresh button) and you will see cached results, because it is more efficient to be done this way.
There's also a certain number of whois queries that an IP is allowed to make in a certain timeframe (again depends on the registry) which makes it not viable for a company/tool to run thousands (or millions) of WHOIS queries every day to every domain that is registered just for the purpose of keeping their data up-to-date.
In short, the tool that will get you the most up-to-date and accurate information is
https://github.com/rfc1036/whois as mentioned by
@Future Sensors - simply put because you're directly querying both registry's and registrar's (when available) whois servers instead of going through a "middleman" that may cache data like domaintools.com.
The tool is not the most user-friendly and may take some time to develop a parser if you're planning to do bulk whois checks, however these type of cases are always a trade-off - you should evaluate what's more valuable to your use case: reliable data or instant results.