I have an 2006 GS430 and love it. Currently, I have 50K miles and the car has been trouble free. I recently replaced the OEM Nitto tires as they were extremely noisy. In June I put a new set of the Michelin Pilot Sport AS Plus tires and the ride is phenominal. My only complaint about the performance has been some issues with the braking as it gets choppy during sudden braking situations. I'm currently looking into purchasing non-OEM rotors, pads, etc. Good luck.

 

I would go for the 06 gs430 since it has the new body style like the 10 models. The car is more responsive than the 06 ls430. It has better pickup off the line. Interior is superb and very modern looking. People complement my car all the time even the guy that has the 05 ls430.
The ls is the flagship car, however, the 06 has the same body style since 01.
You won't be disappointed with the 06 gs430.

 

I would go with the 06 GS430 for sure. Im currently looking for one myself, but haven't found one im completely sold on. I currently have an 02 GS430 and a 05 Infiniti Q45. Someone made a comment about a BMW they had falling apart after warranty... that is why I buy Lexus. Some of the Lexus models have their quirks, but they are far more reliable than any other car after 100,000 miles in my opinion. My first Lexus was an IS300 that I sold with 150,000 miles on it and I would have driven that car anywhere.