echoping, with its default setting, assumes the remote host accepts such connections. Experience show that most Internet routers or hosts do not. Some Unices are not shipped with this service enabled and, anyway, the administrator is always free to close it (I think they shouldn't). echoping has therefore less chance to succeed than ping or bing. (On a typical Unix box, "echo" service is configured in /etc/inetd.conf but see the CERT advisory.)
echoping simply shows the elapsed time, including the time to set up the TCP connection and to transfer the data (but excluding the time for the - possible - DNS call). Therefore, it is unsuitable to physical line raw throughput measures (unlike bing). On the other end, the action it performs are close from a HTTP request and it is meaningful to use it (carefully) to measure Web performances.
On operating systems, like Linux, who have the TCP_INFO option (see a detailed presentation), echoping can also display interesting TCP information.
With UDP servers you can have surprises: the first test is quite often much slower since inetd has to launch the process. After that, the process stays a while so the next texts run faster.
There are many, many traps when measuring something on the Internet. Just one example: 'echoping -w 0 -n 4 a-sunOS-machine' and you'll see the first test succeed in a very short time (if you are close from the machine) and all of the others take a much longer time (one second). With '-w 1' (wait one second between tests, the default), everything works fine: it seems the sockets on SunOS need time to recover :-)
Use all of them with care, the result is not obvious to interpret.
If you are interested in Internet measurements, there is an Internet Engineering Task Force Working Group, IPPM (IP Performance Metrics) which produces many fine RFC that are really good to read. I appreciate RFC 2330 and 3148.
And don't forget to read RFC 1470 ("Tools for Monitoring and Debugging TCP/IP Internets and Interconnected Devices"), specially its "Benchmark" section and the Richard Stevens' books (all of them), published by Addison-Wesley.
Last, but not least, since statistics is typically a very neglected area in computer networks, Basic Statistics is a fery useful resource. For the reasons why echoping displays median as well as average, see Mean Delay Considered Harmful.