Utility
The Lexus GS 450h and the Lexus GS 350 can accommodate the same number of passengers.
Dimensions
The GS 450h is significantly heavier than the Lexus GS 350.
The Lexus GS 450h's tank is roughly the same size as the Lexus GS 350's, though the Lexus GS 350's is somewhat larger.
Cost
As far as gas mileage, the Lexus GS 450h beats the GS 350.
Producing an exact fuel economy evaluation is so tough that some think not even the federal government can do it, but it looks as though the Lexus GS 450h is the winner in terms of gas mileage.
In terms of MSRP, the Lexus GS 450h costs substantially more than the Lexus GS 350.
Handling
With their similar turning circles, the GS 350 and the Lexus GS 450h quite certainly handle roughly the same into and out of tight spots.
Warranty
The GS 350 and the Lexus GS 450h have the same basic after-sale protection.