I have purchased KYB's in the past for my wife's Toyota Corolla and my daughter's Nissan Pathfinder. Quality wise they are good, I just do not like the feel / comfort (they are too stiff).
Recently my rear right strut started to leak really bad, RX330 89,000 miles, and was presented with the same predicament; struts must be replaced in pairs. I did not want to go with KYB because I knew the ride was going to be stiff. So I started looking into Monroe's and heard that they are okay. Someone told me to go to Ebay to look for OEM (Toyota struts), I am glad I listened. I found a deal for a pair of Rear OEM Toyota Struts brand new in the box with Toyota's part number stamped in the box for a little less than $300 delivered. In order to keep my cost down I purchased the strut mounts at Pep Boys and the coil spring insulator's at my local Toyota dealer. Parts directly from Lexus are more expensive and by purchasing at Toyota I save a few bucks. It is recommended to replace strut mounts and insulators when replacing struts. In all it was a 4 hours job with an spring compressor tool i bought at HF.
Hope this helps.