Both CompactRIO and PXI have IO modules and the processing power to capture / process / log for machinery monitoring.
It depends on the number and type of sensors you want to connect, the sample rates and the real-time processing required (e.g. calculate spectra - max frequency, frequency intervals). Once you have that the correct option may become more obvious. An important consideration may be if you require any of the ADC channels to be simultaneous and synchronised - e.g. trying to look at phase shift between neighbouring vibration sensors, or calculating instanteous power from AC volts and current. If you have many signals, then you need to consider if it can be handled in a single chassis, as having signals from multiple distributed chassis is possible, but adds complexity/cost.
We're just finishing a rotating machine test rig, and that is running on a cRIO-9049 8 slot with plenty of FFTs generating spectra in real-time along with many lower sample rate signals for pressure, temps, etc. FPGA/CPU usage is not close to capacity - though sample rates for vibration data is fairly moderate.