So on Saturday BMW was nice enough to let me drive a new 435i with the M-Sport package and even nicer to let me drive the Audi S5 as a point of comparison. Let's set some expectations here. This will not be a professional article with lots of photos and stats for each car, going in-depth, toe-to-toe on each car. This will be my personal account of the two cars driven back-to-back in about an hour total time. The drive was on public roads, not a race track, so I didn't get to push either car too hard. There will also not be a bunch of photos as I wasn't going to be "that guy" and pulling a car aside while others waited to drive it. As long as we're clear, read on.
To provide further context about where I'm coming from, my garage currently contains an E39 M5 and a E46 wagon, so while I might be accused of being a BMW fan-boy (foreshadowing!), I previously owned a B4 S4, several VWs, and a handful of Japanese, American, and Swedish vehicles.
Moving from my 400HP V8 to a 300HP turbo I6 (but lighter car), I wasn't expecting the 435i to blow up my skirt too much, but it gets moving in a hurry. It's like most turbo motors where it really shines once the boost builds, but it never felt like it bogged down too much at lower RPMs. It never kicked my head back like the E39 M5 or E92 M3, as the V8 torque really pushes you back as you jump off the line, but the sensation of speed builds quickly and smoothly until you realize that you'd be in jail if you were in Virginia right now.
The ZF 8-speed box provided very snappy upshifts and the car rev-matched smoothly on downshifts. This is in stark comparison to the 2006 E60 M5 with DSG I considered buying instead of my E39, which made me sea-sick if I wasn't constantly adjusting the shift severity. If I was to actually buy a 435i, I'd be forced to get one with the ZF since my wife refuses to learn stick and as such can't drive my M5, and I would be okay with that. It's still a lot of fun when you want it to be, and not annoying in everyday situations like the DSG and other auto-manuals.... and I guess my wife could drive it too.
The steering is light and responsive, providing nice feedback to the tires. The brakes are stellar, stopping my nicely from 60mph on a downslope without drama. The active suspension is great, keeping the car level through the bends.
As requested by AM3R, the back seat was decently comfortable for all 5'8" of me. Without having one nearby to compare, I'd say it was on-par with the E92 3-series coupe, but not as much room as the current or previous-gen 3-series sedan.
Maybe it's just a power-seat issue I've never faced, but ingress/egress is a bit annoying with both the tab to fold the seat forward and a button to move it forward/back. I'm used to a single pull that would fold the seat and pull it forward to give you plenty of space, but I've also never had a 2+2 with power seats.
Having two small kids (ages 4 and 2) I noticed the (federally-mandated) child-seat latch system in the back. I would not put my kids back there until they were both tall enough to bend their knees over their current seats or be in a booster. Right now they (especially the younger one) constantly has their feet up against the front seats, and with not much room to stretch, those in the front would be subject to constant pushing, which would then result in constant yelling from you to "GET YOUR DIRTY FEET OFF MY NEW SEATS!" Once they are tall enough to have the knees bent 90 degrees you might get some light kicking, but they wouldn't have enough room to get a good swing or push. Those with smaller kids in a rear-facing seat would not have much room for anybody in the front seat and getting the seat in and out would be rough.
Speaking of seats, these are very nicely bolstered (my M5 seats feel like a couch in comparison), but quite firm. I can see long hauls getting a bit uncomfortable. The rest of the cabin is the usual, modern BMW fare. If you've had a BMW from the last 7 years you should be able to find anything you need.
Now onto the S5.
Looks-wise, I prefer the A5/S5/RS5 over the 3/4-series. The big, gaping grill and sharp led running lights looks cleaner and more aggressive to me. The interior is just as nice as the BMW but I didn't have much of a chance to play around inside and see how the infotainment and controls matched up. The seats in the Audi were not as heavily bolstered as the BMW, but much more comfortable for daily use.
One control that Audi (and VW) still haven't got right is the manual shift direction is backwards. Upshifts should be towards the rear of the car, downshifts forward. Sequential gearboxes in race cars are this way because acceleration is pushing you back so if you need to push forward to upshift (like in the Audi) you are fighting gravity with your arm. It's been this way for years and VW/Audi still refuse (HOW DARE THEY IGNORE MY COUNTLESS LETTERS!) to switch it the right way.
Other gripe of mine, that has been an issue in VW/Audis since at least 2005 (based on my experience, could have been earlier) is the brakes are way over-powered. Not over-powered as in, "holy crap I can stop from 60mph in 10 feet," but over-powered as in, "I lightly touch the pedal and my chin touches my sternum." The brake pedal in this car has almost zero play and the brakes grab hard immediately. It takes some getting used to not to jerk forward when coming to a stop. It was the same on my A5 Jetta and the Tiguan, and it always took me a bit to get used to when switching to those cars from mine.
The engine in the S5 is the winner between the two. Better low-end grunt makes it feel faster around town, though the BMW is just about as fast to 60mph (I believe they're about 0.1 seconds apart). You feel the turbos climb on less in this car. Not sure if that's due to the twin turbos vs. progressive turbos, V6 vs. I6, all of the above, or none of the above. [UPDATE:] Der... I haven't been keeping up and forgot they switched from twin-turbo to supercharged. That's why I didn't notice the turbos and why the low-end torque was better on the Audi. [/UPDATE]
In the few corners I got to go a little faster, I could feel the Quattro clawing at the road, trying to offset the understeer. The steering is much heavier and provides less feedback than the BMW as well.
Overall, I'd rate the 435i as much more of a "driver's car" than the S5. With the M package I drove, I'm not sure it would be great as a daily driver, more of a weekend car (with some AX and track days thrown in), while the S5 could be used every day without complaint.