Which Perl module would you recommend for JSON manipulation?

JSON module works like a champ, but if you need a faster parser, use this one: JSON::XS, which requires a native compilation.

Note that JSON version 2.0 and above is merely a front end for JSON::XS (if installed) or JSON::PP (fallback).

[Update: I now recommend Cpanel::JSON::XS over JSON::XS. Cpanel::JSON::XS is a better maintained version of JSON::XS.]

I always use JSON::XS. Complete, robust, proven, fast*, easy to use, and even a bit of flexibility if you need it.

It's probably the most used JSON parser, though most access it through JSON (but doing so risks using slower JSON::PP instead).

* — "An order of magnitude" faster than JSON::Tiny, according to JSON::Tiny's docs.