The "good" and "reliable" remailers are the ones that work for you and
have the feature set you need or want. The "secure" remailers are the
ones operated by those who do not monitor the traffic passing through
them AND have good security policies in place on their networks and
machinery to prevent their remailer from being penetrated by
unauthorized parties and subsequently compromised.

Since you can never know for yourself how "secure" any one individual
remailer is, you should always use encrypted chains of remailers (see
#4.3) to send your messages. So long as all the remailers in your
chain have not been compromised or their operators are not cooperating
amongst themselves, then your traffic will be reasonably secure.

Advanced topics relating to traffic analysis of the remailer network
that may allow adversaries to deduce the source and destination of
individual messages is, for now, beyond the scope of this FAQ.
However, it is almost certain that these activities do take place to
some degree. It is for this reason that you we have advanced remailer
protocols such as Mixmaster, and proposals for other up-and-coming
network scenarios (like WOF <http://www.bigfoot.com/~potatoware/wof/>,
RadioClash <http://piratech.net/radioclash/>, Publius
<http://www.cs.nyu.edu/~waldman/publius/>, Freenet
<http://freenet.sourceforge.net/>) to reduce the effectiveness of
traffic analysis.