What is the difference between an SiDi engine and an ordinary engine?

Basically, the difference is that in SIDI, you have Direct Injection, meaning that the fuel injectors squirt the petrol directly into the cylinder, rather than into the intake port. This gives a more complete, more efficient combustion and allows the engineers to increase compression, lean the fuel mixtures and make a whole bunch of other changes to improve fuel economy, increase power and reduce emissions.

True; however, DI creates a carbon build up problem on the intake valves. You know, like the class action lawsuits against Ford's V6 DI engines.

which Cadillac CTS model is the best to purchase, the DI or SIDI?