So to be specific to those who drove both or are knowledgeable. How would a 2010 compare to a 2013?
If one was 8k and the other 13k with same milage what would you get?

 

2013 better by far, a newer generation, a bit larger and more creature comforts. That being said, a 2014 might be better, the 13 was the first year. But I have nothing at hand that proves that.
And, of course, it depends on condition, and history of each specific vehicle.

 

>more creature comforts.
No comparison, #5 was much more Toyota-like while #6 is a "true" Lexus all the way (but, hey, seriously, that's a bit of an exaggeration since the LS, for instance, is a world apart, but was also 2X+ the cost, no way to capture all of that in the price range of an ES, but you know that you're fishing in the same pond).
The biggest change is the #6 has the back seat of a limo. Three full sized adults can fit comfortably, with plenty of leg room, back there.
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My karma just ran over your dogma
Current Hers: '13 Lexus ES350
Current Mine: '15 Jaguar XF (it's aubergine)

 

Hmm, so $5000 difference. The 2013 will have a nicer interior and parts will be 3 years newer, I guess I would ask myself if I had a 2010 would I pay $5000 to upgrade all those things. It may be that any way you slice it you will not get to the $5K unless you add in the happiness that the upgrades and having a newer car gives you.

 

The Generation 6 2013 ES shares its platform of the Toyota Avalon. The Generation 5 2010 ES shares its platform with the Toyota Camry. The difference between the larger Avalon based Generation 6 ES, compared to the Camry based 2010 ES, will be most noticeable with regard to having more interior space, especially with back seat leg room.

The 2013 ES, being 3 years newer and with a newer generation will have newer technology which results in a newer generation navigation system, Bluetooth support, etc.

With regard to interior styling, it is a subjective choice with regard to which is nicer. For me, I prefer the more classic luxury look of the Generation 5 ES over the interior styling of the Generation 6 ES. And the Generation 6 interior has more plastic hard surfaces and, to me, a lower quality of interior materials than the Generation 5 ES. (But, after the mid-cycle re-fresh done to the Generation 6 ES with the 2016 model year, the 2016-2018 ES interior received a very nice face lift that gave it a more upscale feel and look.)

Even though the 2010 ES is now 10 years old, I think that a well-maintained 2010 ES is still a very nice looking car, and, as I said, I prefer the more classic look of the interior of the Gerneration 5 ES. But, all things considered, the 2013 ES is a better car, and it would be my choice.