After owning both cars for over three months, I'm able to come to a conclusion on this question. And the answer is not entirely clear because on any given day I can say it depends on my mood. That sounds silly, but to a degree it does matter what mood I'm in- and maybe what mood you might be in when you get behind the wheel as to what you are looking to get out of your car that day.
Are you looking for excitement, an easy drive to the store or something in between? My explanation below will hopefully shed light on the personality of each of these cars and are they direct competitors.
The bottom line is both the cars are miles ahead of where cars of this class were 5 years ago. The technology, the safety systems, handling, economy and quality are far better. Of course prices have gone up, but you are getting quite a lot for your money. For example, The Elantra N with the DCT at $35,000. feels every bit as good as my 2017 Alfa Romeo Giulia Ti Sport that cost $46,000. 5 years ago. To think a Hyundai could compete performance wise with a far classier and more premium car as the Giulia is insane- but true. Also the new Civic Si delivers 40+ MPG consistently, while providing all the power most people will need on the street and handling that compares with many sports cars. ( Take that note from a Porsche Cayman owner that says he got beat in an autocross by a Civic more than once)
So here's my overall driving impressions. Civic Si - Feels light and nimble with a small turning circle. The car is not fast coming off the line with its 200 HP but it revs freely and gets stronger as the revs climb. It rides firm but not harsh and it is a masterpiece when taking turns. The limited slip differential pulls you out of corners and there's almost no oversteer until pushing the limits. It corners flat, feeling very planted and the seats are as good as you will find in cars far more expensive.
It is very easy to drive slow and smooth with a shifter as smooth as butter. (Every bit as good as my Porsche Boxster) You can take your wife or kids for a ride and they don't know you have a Go Kart sitting under you. Driving fast is a blast and the car makes you feel like a pro. It makes you look and feel good and there's even a little bit of engine sound pumped into the cabin to make it exciting.
For a sticker price of $28,595. (destination charge included) it is a great value in today's market. Dealer markups are the norm right now with $2,000 - $4,000. being the current situation. Still well worth it when you consider you can easily get 40MPG and have a fun, attractive and practical car to drive!
Elantra N - I'm implying these cars compete in the same space and to a degree they do but at $35,415. (including destination charge) the "N" is a half step up. Dealers are also marking these up but the markups tend to be more in the $1,000. - $3,000 range with a few owners reporting they bought at MSRP with only a few required dealer installed options.
The difference in the driving is pronounced. The "N" feels and sounds much more muscular, because it is. With 276 HP it wins but the car is also about 300 pounds heavier with the automatic transmission, which I have. It feels like a bigger car, yet the exterior dimentions are nearly identical as is the wheelbase. When driving the car you notice the chassis is stiffer and the ride surprisingly supple when in Eco mode. And here's a big difference, the car has an adaptive suspension. When in Sport mode or N mode everything stiffens up and you go from family car to race car with the push of a button! The one thing I do notice, for all its race car like qualities, the turning radius is bigger than the Honda's so you feel like you are driving a bigger car despite them being the same size.
From a thrill standpoint the Hyundai 'N' wins hands down. The active exhaust valves open in Sport and N modes and you get pops and cracks like gunfire. You really have to be careful where you deploy this little 'firecraker' because we know of one owner being ticketed for the car being too loud. My advice- head for a country road and pop and bang to your hearts content- guaranteed to make you smile!
From a handling standpoint, the 'N' also wins as Hyundai has the superior suspension that is more track focused. In fact some car reviews put it on the same level for handling as the Si's big brother, the Type R. The seats are very much like the Honda's, well bolstered and very comfortable. I do like the interior seat materials better in the Hyundai, yet the plastics look and feel cheaper than in the Honda so it's a draw when rating the interiors. Visibility out of both cars is excellent and by removing the rear seat headrests in the Hyundai, the view out the back is better in the "N".
So to sum up, I give the edge to the Hyundai in spite of the additional cost. It is a $50,000. performance sedan for $35,000. while the Honda is so good at around $30,000. it still is a half step below the "N" car. Which would you buy? It all depends on your budget and the last factor- looks. The Honda is eye candy for anyone while the Elantra N is something that grows on you. I love the rear 3/4 view and I'm beginning to like the front view as I get used to seeing it. Everyone has an opinion on it- you either like it or you don't.
Only time will tell which one wins out. Will the "N" car culture grow and become a classic like the Civic Si? What do you think?