I just went from the TRD 1st Gen CAI to the URD
The TRD is well built and sturdy only issue i had with it was the air inlet is in the fender well and with having fender flares and no liner it was causing build up of dust and dirt with was causing excess cleaning and replacement of the filter also a possibility of hydro-lock (in my case). Good sound and better pick up from stock and was on the truck for 51k
My current cai is the URD, it takes a little mechanical know how to put it in you have to cut a larger opening for the inlet piping you must also extend your maf sensor so you must know how to solder or know someone who does. Yes there is the possibility of hydro-lock if you live in a overly wet place but they sell pre-filters for this issue. Awesome sound with the URD and better performance on the truck for about 500 miles
this is my personal option.
the URD is far better then the TRD. Ive had the URD for going on 2 weeks and the the truck performs better, has more pick up and sound 80x better. Like previously stated if you live in an overly wet place u will need a pre-filter.