The Trackman 4 and GCQuad are priced in a similar range and are commonly compared to each other. This is due to that similar high price but also because they both are out to be the leader in the same space. They are not after mass adoption like some other cheaper launch monitors but they are after the true professional golfers who want to focus on fine tuning their swing and those who get into the data of their club swings and ball flight. Right now it seems that the consensus is that the Trackman is the leader in this space. It is essentially used by every single pro right now while the GCQuad is used by some of the pros but doesn't have the full trust of the majority like the Trackman does.
Both of these manufacturers claim that they have the most accurate launch monitors in the industry. While one can’t be telling the truth it is really hard to say which one is actually more accurate. These launch monitors both use cameras to get the most accuracy possible but the Trackman uses doppler radar technology as well. Some people feel that lasers give more accuracy than radar but the Trackman has found a way to make theirs exceptionally well, using radar technology. It could come down to a personal preference of what technology you find is more accurate to decide if you want to use the Trackman or GCQuad.
These both have essentially the same features. If there was a tie it would be in the features that they offer. Where the real tie breaker may come in is in the technology that they each use to get their data and the price. The GCQuad is a bit more affordable and does offer a similar product. If you are interested in a simulator that is this expensive it won’t matter as much to you probably to save a few thousand going for one or another tough. What matters is the accuracy and what you are comfortable with.
Both of these will provide real time data after every swing. There are also logs of data that can be reviewed after the fact. It is not without reason that professionals use the Trackman and even some have begun to use the GCQuad now as well. They both give exceptional data that can’t be found with other golf simulators.
When it comes down to it the price, technology, and comfortability between the two models are really the only differences. If one of those or two of those matter more to you than the other, that one could be a good fit for you. Experiment playing on these simulators to see which one you think tracks your specific swing and shot the best before making a choice.