The second kit (Aisin) would be my choice...YOu basically want the Aisin waterpump, Koyo bearings, and Mitsoboshi timing belt...they are all original equipment manufactorers. I just did this on my RX400H...Made a crankshaft pully removeal tool and went to town...the hardest thing was holding the rear cam in position when tensioning...Save yourself a lot of headache and make sure to removed the windshield wiper cowl assembly...it gives you the necessary room to work on the engine....There is a lEXUS rx300 U TUBE VIDEO ON THE PROCEDURE WHICH IS basically the same as our cars, except we dont have to remove air/conditioning pump, power steering etc... Please note the Aisin, koyo, and Mitsoboshi are the brands of choice... I know it is more, but you dont want to do this twice....here is a thread from Club Lexus that shows the tool that I made...
http://www.clublexus.com/forums/rx-second-generation/579348-timing-belt-change-nightmare.html