If its referring to a restorative material, the best would be calicium hydroxide as well as GIC..

Calcium hydroxide–High potency as an antibiotic..in relation to endodontics
–It helps in formation of reparative dentin in IPC and deep cavities

GIC–best material as a restoration especially in pedo thanks to its anti-cariogenic properties [fluoride release]
–though compressive strength was deemed low and was not indicated in classs2 in permanenet teeth now high strength restorative GIC is also available

Of course both these materials have many advantageous properties,these are a few in terms of clinical use.

CAVITY SEALERS:
These materials provide protective coating to the walls of the prepared cavity.They are applied to the walls of the prepared cavity to seal the interface between the restoration and the tooth.
eg-CAVITY VARNISH, RESIN BONDING AGENTS

CAVITY LINERS:
These are cement coatings of minimal thickness, which serves as a physical barrier effects to bacteria.They also provide some therapeutic effects such as fluoride release, antibacterial effect etc.The liner is applied usually only on dentinal walls of the preparation close to the pulp.
eg-CALCIUM HYDROXIDE, GIC

CAVITY BASES:
These are materials that are used to replace missing dentin or to block out undercuts in preparations for indirect restorations. They provide thermal protection for the pulp They are placed in thickness of about 0.5-2mm & exhibit adequate strength to support the overlying restoration.
Bases are applied on pulpal and axial walls of cavity restoration.
eg-ZN-PHOSPHATE CEMENT, GIC [TYPE III] , ZN-POLYCARBOXYLATE CEMENT