There is a great document titled Evaluating PXI and VXI Platforms for your Measurement and Automation Needs which discusses the differences between VXI and PXI. When it comes to market trend the PXI platform is a better choice because it builds upon more modern technologies such as PCI and Plug and Play configurations so it will continue to grow in the market. The VXI met goals that were set by standards in 1987 so it is an older technology.
First of all, thanks for your help. Can you direct me to a similar article that compares VME, cPCI & ATCA?