I drove 2 different Ascents (Premium and Limited) over two years and have now settled on a 2021 Highlander Hybrid Platinum. I am very happy with my new car. Major differences that I notice with the Ascent vs Highlander are slow speed driving smoothness, suspension and handling. The Highlander wins on all three handily in my opinion. I always felt like the Ascent was lurching slightly at slow speeds, especially when doing the first shift into drive after backing out of driveway and alse whenever I took my foot off accelerator. Not the case with the Highlander. It is smooth as butter! Likewise, the suspension in the Ascent seemed kinda clunky to me. Small bumps would often send a big sound and feel through the cabin. The Highlander is WAY more refined in the suspension and just floats over smaller bumps. The Highlander feels a lot more planted on the road with far less body roll and more predictable manners while cornering. I feel a lot more confident taking a curve at 50 miles per hour with this thing. Overall the Highlander is just a more refined machine. The Ascent needs some tweaking to bring it up to snuff. I should also mention that I think the interior quality is a step above the Ascent. Seats in my Platinum are much more comfortable that Ascents and the leather just has a nicer look. This Platinum has a luxury level interior whereas the Ascent didn't quite get there. The JBL sound system in Highlander is just clearer and sounds more HiFi than the upgraded Harmon Kardon stereo I had in the Ascent Limited.
True, the Highlander doesn't have full-time AWD, but AWD is still very much there for power boosts and when traction is compromised. The second electric motor that powers the rear wheels kicks on immediately when it detects slippage. I don't necessarily want or need all four wheels to be turning (and burning extra fuel) all the time. I drive mainly in an urban/suburban environment in Portland, OR with a lot of hills, and this Highlander really seems like the ideal SUV for this environment. When I go up to the mountain, I know that the AWD will work nicely, and I believe that the Trail mode will provide better traction when you need it. You should note that the Ascent doesn't have any driving modes, while the Highlander has 5 (eco, normal, sport, EV and Trail). This is handy and just makes driving more engaging.
I highly recommend the Highlander Hybrid if you want one of the most refined crossover SUVs with excellent gas mileage and don't necessarily need AWD for off-roading or what not. One area where I think the Ascent has the Highlander beat is it that it is probably slightly more off-road worthy. I will save approximately 200 gallons a year in gas with this new car or approximately 2 TONS of CO2 emissions (I drive about 8k per year). Imagine if all 80,000 Ascents sold last year where instead Highlander Hybrids? That would save about 25,000,000 gallons of gas or 250,000 tons of CO2 emissions. That volume of gasoline is enough to cover three football fields 25 feet deep with gasoline. The larger impact of choosing and efficient vehicle is something to consider. After driving a Prius for 5 years from 2010-2015, I could never really get over the extreme loss in economy with the Subarus.