As for Pix4D, I find that it is the most powerful processing software. I have also tested DroneDeploy and MapsMadeEasy. They all have their advantages and disadvantages. Pix4D allows me more processing options than the other web based engines, but requires a strong computer. As for price, the Pix4D is expensive, especially for a startup company. I wish they had a points based program like MapsMadeEasy.
Of these three that I have tested, they all give different results with orthomosiacs, which is what I am after. Sometimes the MME looks better, and sometimes the DD looks better. But almost always, the Pix4D looks the best. It seems to model the vertical edges and cut through trees better than the others.
So depending on what you are trying to produce, you will just have to test all the options and decide which is best for you. For survey grade orthomosiacs, the Pix4D allows the necessary options, like GCP , camera , and rolling shutter corrections. There is a steep learning curve, but the training videos are very helpful. I hope to have enough paying jobs to afford Pix4D soon, since my trial periods have ended. -JMO