No one seems to have mentioned a very important aspect of this. The bandwidth and CPU requirements for either of these depend greatly on the type of compression and the amount of compression used by the server. (The settings are determined by the server you are connected to.) You get a lot of people with varying opinions on the amount of lag/ping issues, speech quality, etc., but they are not taking into account the server settings.
It's been a while since I've setup a TS server, but I have a Ventrilo server running. I'm not sure about TS, but Ventrilo has several types of compression and many levels within those types.
Speex is the compression most often used with Ventrilo. The sample rate and number of bits can be varied over a broad range. Most rentable servers default to a rather low compression (high quality) setting, but a support ticket can usually get them to crank it down a notch.
(My Vent server (version 3) is currently running Speex at 16kHz, 16bit, 5 Qlty which seems to be a good compromise between voice quality and bandwidth usage.)
That being said, after using both, I generally find the voice quality of TS to be inferior to Ventrilo. (But you can set Ventrilo to some awful quality if you want

)