We currently install all of ODL to /opt/opendaylight. This works and follows best practices, but it's possible to follow better best practices by installing various parts of ODL to various parts of the filesystem.

JankiChhatbar gave me this better best practice summary:

• configs go to /etc/programName.conf file and/or /etc/programName.d dir.
• libraries to /usr/lib and/or /usr/lib64
• binary / binaries to /usr/bin or /usr/sbin
• documentation / manpages to /usr/share (that shall rather have platform independent content while binaries are often compiled just for a given platform - but in case your binaries can run on more platforms, you can put them there - likewise sos on multi-platform python does)
• runtime data to /var/lib/programName
• logs under /var/log/ (and/or syslog/journal)