I've considered the 2018 Camry and a year old used ES350, but purchased an Avalon. Imo Toyota wanted to distant the 2018 Camry away from the Lexus and Avalon as far as possible and they sure succeeded. It's a nice car, but it ain't what I was expecting after all that talk about comfort, luxury interior and sophisticated powertrain. I've driven only an I-4 LE and SE and while the new 2.5 feels pretty nice, the 8-speed tranny was too sluggish and busy to my taste, but the biggest issue I have with the 2018 Camry is the lower sitting position and lower roof line. Even though they say the 2018 interior got bigger, it feels like it has less usable space vs the gen 7 Camry.
I drove a 2015-16 and 2017 ES350 and I would call the 2016+ Avalon more Lexus than ES350 is. Yes, the ES has a nicer center console and a bit nicer door cards and I love an analog clock in the middle, but the center tunnel looks and feels unacceptably cheap, so much hard plastic is ok for a Corolla-Camry level car, but not for a $40K entry luxury car.
The Avalon's touch screen is easier and quicker to operate (or just set it to auto and you don't have to touch it at all) and all center dash controls have much better ergonomics vs the ES's mouse pad and slippery wood steering wheel is so 90's.... The Avalon has more front and rear room and more comfortable on less than perfect pavement and there is no noticeable road and cabin noise difference between the restyled ES and 2016+ Avalon. The ES drives a bit sportier (most likely due to 18" wheels), but has pretty average cornering stability, though neither the Avalon or ES are boats and can be driven in a spirited manner. The MPG is the same, since the powertrain and all other specs are identical.
I feel very comfy in the Avalon and ES. I was pretty comfy in the gen 7 too, but can't say that about the 2018. The sitting position, seats, arm rest- everything is more comfortable in the Avalon. The comfort, ride, interior roominess and interior materials wise the Avalon and ES are in a different league compared to the 2018. The seat cushion angle was not sharp enough to me and I had to put rubber spacers under the front of the seat frame to fix it, but besides that the seat is really really comfy.
The Avalon's exterior is more stylish, though the C-pillar-trunk lid line is too hatchbackish imo and if want a sportier ride try a Touring model. They improved the ES front end look, but rear end still looks very average. Imo due to the lower design and huge windows he 2018 looks disproportional and while its front end is way too overdesigned, the rear is very simple and characterless.
Lexus has a better brand image, no arguing here, but in case with the ES350, since it's one of the most mass produced, most affordable and most discounted models, the ES image is not that high. My relatives own an IS,GS, ES and RX and I have very high opinion about the restyled ES, but since the Avalon got more comfortable and nicer detailed, I see no reason to pay an extra 5-7K for a badge. The GS is a different story and unfortunately significantly more expensive.
My buddy got an Avalon XLE Premium with bunch of add ons for $31K +TTL. Mine with less options was 30K. A similarly equipped used restyled ES350's were around 37K. It's hard to find a nice a year-2 old ES cuz all nice units are getting picked up and certified by Lexus.
There is another thing about the ES and Avalon. Both cars are at the end of their production life and will be replaced in 2019. The Avalon will be replaced by the new TNGA based Avalon, but the ES most likely gonna be discontinued. Looks like Lexus is planning to kill the ES and GS and introduce a new model that should replace them both. In that case they would drop the ES name and call it something else. No matter how good is a car, when a model is discontinued or even renamed, the resale of the older model goes down and unfortunately the ES's resale is not that great anyway (neither the Avalon's or Camry's, especially loaded XLE and XSE resale) compared to 5-7 years ago, but since the ES is noticeably more expensive, it would lose more.
If you can afford a nice ES- go for it, but if not, the Avalon is more than capable to deliver everything that the ES350 can, well, besides Lexus brand image.
