Handling
With its tighter turning circle, the IS 350 is definitely more maneuverable than the Lexus ES 350, something to consider if you do a lot of city driving; however, remember that a vehicle with a tight turning circle may feel a bit twitchy on the highway.
Drivetrain
The Lexus ES 350's engine isn't much larger than the Lexus IS 350's.
Torque is the force that lets you accelerate quickly, and in this respect, the Lexus IS 350 isn't much more powerful than the Lexus ES 350.
Utility
The Lexus IS 350 and the Lexus ES 350 can accommodate the same number of passengers.
Convenience
You will most certainly have to visit your friendly gas station more often with the IS 350 than with the Lexus ES 350.
Comfort
While the front cabin in the ES 350 offers a bit more head room than the Lexus IS 350, there really isn't much of a difference.
The ampler interior dimensions of the Lexus ES 350 make it substantially more spacious for your passengers than the Lexus IS 350.
Dimensions
The Lexus IS 350's tank is approximately the same size as the Lexus ES 350's, though the Lexus ES 350's is slightly bigger.
The IS 350 and the ES 350 compete for the same parking spaces.
Cost
The Lexus IS 350 doesn't pale in comparison to the Lexus ES 350 in terms of fuel economy.
With respect to gas mileage, the Lexus ES 350 and the Lexus IS 350 don't differ much.
The Lexus IS 350 isn't much more expensive than the Lexus ES 350 when it comes to MSRP.
Warranty
The ES 350 and the Lexus IS 350 have the same basic after-sale protection.