silent is a VERY relative and subjective term. for the purist, silent means 0db
but for most people, silent generally means noise level that can easily be ignored in a room with very low ambient noise(not a living room or somewhere that have other noise sources other then an air conditioning vent)
of the cases you have selected, the FT02/RV02 will have the best "filtered" CFM per decibel performance. other cases can approach that performance, but only with after market fans which adds to the overall cost of the solution...
personally, i'd recommend a RV02-E with a rheosmart6 fan controller for the most ideal configuration while being somewhat cost conscious. the RV02-E has the same internal structure as the FT02 so thermal and acoustical performance should be very close but cost about 20 to 30% less then the FT02
with the AP181 fans on low and hooked up to the rheosmart6 on automatic setting, the FT02/RV02 is easily quieter then your air conditioning vent and therefor easily ignored by most ears.