There are two approaches to reinforcing concrete. The traditional method uses re-bar or metal mesh to hold concrete together. The newer approach is to mix fiberglass with the cement (applicable only to slab pours). Fiberglass reinforced concrete resists spalding, chipping and hairline cracking better than metal reinforced concrete. You will be able to see the fiber in the finished slab. This saves labor because no metal is laid and tied.
Metal reinforced concrete holds together better if major cracking or movement occurs and is really your only option (code approval) for foundations, stemwalls curbs and stairs.
If your foundation for the slab is good and solid and you don't expect major settling, get the fiber reinforced concrete. If you expect something may settle, or you are subject to significant ground movement (clay soils, freezing temps) go for the metal.