The Vex IQ brain has some advantages over Lego p bricks. It has 12 I/O ports and is less expensive. One disadvantage is that Vex IQ has fewer commercial sensors available for it. This being said I have managed to hack the Vex IQ bumper switch so that I can use it with my robot pain system. Multiplexers can allow me to connect a large number of pain sensors as needed.
Some effort has been devoted to building robots using integrated Lego and Vex IQ components. I have, for instance, bolted Vex IQ plates (4X_ ) to Lego plates and Lego bricks (1X_). One can then build onto this in both directions using both Lego and Vex IQ parts.