The side impact reports for the Regal and Optima are the same.
So now can we move on to long term durability?
They may crash the same but the public preception will be different if they compare. Most people go by how things sound and feel vs how they rate.
As for long term that is to be determind. Based on the past GM cars and Hyundai I would give GM an edge here. They may not all look pretty but many are still on the road 25 years later in the harshest weather areas of out country. When was the last time you saw a 20 year old Hyundai in the midwest? I mean even one that is just park in a drive way disabled? Now how many Corisca, Lumina's, Baretta's, GM H bodies etc to you still see rolling along?
I have have several friends dump they Hyundais well before the warranty was out as they were just having too many issues with non warranty parts. Two lone dumped them for used HHR's and could not have been happier.
Hyundia has improved over the early years but they do save cost in many areas and it does catch up with the cars. GM cut corners in the past with paint and interior. THey did invest well in drivetrains and the old cars show this as the interior looks like crap but the car keep on running and running with little issues.
Well, only have experience with just the one, but I'm driving a Sonata with almost 90K miles on it now and the only problem it's ever been taken in for was the compressor went. I can't tell you how many "little" things the Lucerne has had to go back for in its 55K miles... including its most recent one, cables dangling by the rear wheels under the car on the driver side because a clip broke.