--prefix to /usr/local or /opt?

Solution 1:

The FHS says:

A package to be installed in /opt must locate its static files in a separate /opt/ or /opt/ directory tree, where is a name that describes the software package and is the provider's LANANA registered name.

while /usr/local hold the usual /bin/, /lib, /etc, ... hierarchy

Solution 2:

I use /usr/local for stuff I put into the system, and I let third-party installers take /opt.

Solution 3:

Personally, I like to install everything I build from source in /opt, and edit my $PATH accordingly. It instils a sense of (semi-) cleanliness, and it's easier to traverse the folder structure, perform updates etc. It just comes down to personal preference; one is not necessarily better than the other (just like you said, a style issue).