The CTO and CTS series gels have the both have the same amount of color temprature correction power (e.g. a 1/2 CTO and 1/2 CTS gel will both convert 5000K to approximately 3800K), so they will both correct for Tungsten lighting casts equally well. The only real difference between them is that the CTO has a bit more red, and CTS has a bit more yellow...
From a portrait photographer's point of view the practical usability difference is that CTO will tend to give subjects a bit of a tanned look (depending on the strength of the CTO gel), whereas a CTS will not. My personal 'rule of thumb' is to use CTO on pale subjects who I want to add a bit of 'healthy glow' to, and CTS on folks who already have a tan, and don't need any additional help in that department. :-)