TL has much better support and can be used on some other cars. The newest version takes a bit better lap top and has a slick windows format. It connects to the aldl port and is normally more stable.
Its drawback is that it presents a data sample approximately once every 1.4 seconds.
DS connection requires that the ecm be opened and the engineering port on the bottom of the board be accessed and cleaned for a connector. This connection can be flaky and cause problems at times. Those of us that use it grow to recognize the problems and deal with it.
The real strength of DS is that one can obtain up to 18 samples per second of data which can be useful in tuning very fast cars.
For someone that is learning the cars and trying to understand what is going on, I think TL is the better buy due to its documentation and the strong user support provided by Ken Mosher.