I have not driven the Mercedes but I have driven the Ioniq. It was a very nice vehicle. The showstopper for me was that it had no rear wiper. This seems like a minor thing, but I live in a part of New England where half of the roads are unpaved and during the winter the paved roads are heavily salted, so a wiper really is a necessity. The newest model now has this, but I already pulled the trigger on a new vehicle.
I ended up buying a Chevy Bolt during its final model year. This may be more of a reflection of my own history of buying inexpensive vehicles, but it is the best vehicle I have ever owned. I could not get over the price of the Ioniq. I just needed something that got me from point A to point B, and I wanted something that did so without gasoline. The Bolt far surpassed my requirements, and it was affordable. Honestly, I avoided American-made vehicles for a long time, having had bad experiences with the unreliability of a sequence of Dodges and Fords when I was younger. The Bolt changed my opinion about Chevrolet, although the CarPlay situation is pretty tragic…
FWIW, we bought an Ioniq 5 last spring, live in Michigan, and the lack of a rear wiper has been a non-issue completely. However, and this is a big caveat, I like the rearview camera and never use my rearview mirror as a mirror. Some people prefer the mirror, since the camera display requires you to shift your field of view in a weird way, and if you like the mirror, then the lack of a wiper would be a big deal. For me, I completely forget there is no rear wiper, and actually prefer it now as it makes cleaning snow off a tad bit easier!
I've had an Ioniq since last spring, and while I briefly looked at the Mercedes, it was never a serious contender for me given its cost. The ioniq is awesome, though. The only complaints I have are really minor. Now, part of my love for the car is that it is my first EV, and EVs are just way better than ICE cars - except for the range issue, and we just drive around town 99% of the time, so that's a non issue. It is just so much simpler, powerful, and fun than I expected.
The ioniq 5, specifically, is great, although I kind of wish we would've waited for the 2025 model. I like physical buttons (which is one of the reason I like the Ioniq) and the 2025 model added some more. Plus it has wireless Android Auto, and a few other nice improvements.
Oh, the only actual complaint, still minor, is that it's turning radius isn't the greatest. That's really the only thing that bugs me about it.
Have no hands-on experience with EQS, other than that it stands next to my door (neighbour's), but EQS is huge, costs 2x Ionic 5, has a 100 kWh battery, aerodynamics of a brick, presumably better suspension... a completely different segment.
I way looking at Ionic 5, but it was shortly before the facelift, so I could not even configure it anymore. Got a VW ID.7, very happy with it.
Both Kia and VW latest models do well against Teslas on range/battery (see the 2025 ID4 or EV models from Kia) e.g.