Where steel, or any other material, and concrete must be used to erect infrastructures, their quality is of tremendous importance for a better life service of the said infrastructures, hence the necessity to demand for higher strength and better corrosion resistance materials.
Therefore, a better quality control of bars, TMT ones in particular, is essential. The TM-Ring test ensures that the quality control is actually effective. However, the crack resistance of TMT bars must be checked before being used to make the shear stirrups. Although stainless steels offer good resistance to corrosion, when used in combination with other steels, make sure that the possible galvanic corrosion is minimal.
There is a plethora of rebars, some of which are worth mentioning, notably:

galvanized steel rebars, fusion bonded epoxy (FBE) coated bars,
Cement-Polymer-Composite (CPC) coated rebars, and
Fiber Reinforced Polymer (FRP) rebars.

Galvanized steel rebars can exhibit:

higher chloride threshold,
a wider PH passivation range, and
a lower corrosion rate.

FBE rebars can, in the presence of damage, exhibit moisture-induced corrosion and their exposure to sun can crack their coating.
As for CPC coated rebars, any coating applied on rusted steel surface of theirs may lead to micro-cracks at the interface, resulting to corrosion initiation and propagation. FRP rebars may not corrode, but other chemical attacks are possible and must be taken into consideration.    
The corrosion mechanisms in pre-tensioned system is different from those of the post-tensioned system, and prestressed concrete can be more vulnerable to corrosion and lead to a catastrophic failure. Good grouting practices are very important to ensure durability of post-tensioned structures.