Good luck - but I'm sure the board would appreciate a quick comparison of the your impression of driving a Lexus vs a Sonata. I nearly bought a used Lexus RX350 (wife thinks used is beneath her so that's why we ended up with a new SFS, her car) to me the Lexus has a very solid feel overall , smoother quieter and much better driving dynamics - as it should as they cost more but perhaps the biggest plus to long term ownership is the dependability/reliability you get from Lexus/Toyota ownership.
it's definitely quieter, and has slightly less cabin vibrations than the Sonata, (2GR-FE V6 engine smoothness probably helps),
when going over the bumps, I didn't notice that much difference but that could be due to the higher sidewall tires on the Sonata, (I had 205/65/16 tires in the Sonata, and the ES has 215/55/17 tires)
I don't really care all that much about power, 0-60 times and handling prowess when driving.
are the differences significant enough to justify $20K (approx) differences in MSRP?
personally, no, as I think Hyundai products (despite some reliability concerns) still have great value,
but if one is comparing used vehicles, I think the differences may be worth the extra $5k (approx)
If I had more money to spend, I would have considered the 2015 Hyundai Genesis