It's hard to say what is the fastest, as it will depend on what data you have, how your datastructure looks like and how much data we are talking about. Possibilities include:

• Use a database. Probably not going to be the fastest, but it might. But it's very reliable.
• Use one of the serialize modules available: Data::Dumper, Storable, YAML. If you want something that's human editable, YAML may be your best choice (it would be mine if editability is an issue).
• Use *dbm files. Less suitable if the datastructure is complex.
• Use a "generic" format such as XML, Config::General or one of the other Config::* modules. Perhaps not the fastest, but a smart choice here could score big points in the editability requirement.
• Handroll something. Requires the most work, but (in theory) gives you the best runtime/editability requirement trade-off as you can tailor it to your problem domain.