In the dry, the M135i will be the quicker car. Will be the more interactive and more fun to drive.
However, the appeal of the S3 is that no matter what the weather, it'll go just as quickly thanks to AWD. The build quality, textures, and ergonomics are in the Audi's favour. For me the A3/S3 interior is best in class, by some margin.
Unless you need a Hatchback, look at the Saloons. They look even better.
Things to look out for, to make the S3 feel more special? Super Sport seats, Extended mano pur, B&O sound system, and comfort pack, which give you cruise control, and a few other bits that I can't quite remember.
For me as an overall package, the S3 beats the M135i. But it just depends on your own preference.
I wouldn't focus too much on the pops and farts from the exhaust, as a simple aftermarket system can give you the sound you need. But I think it's the FL 2017 onward S3 that come standard with the pops and farts.
Most people seem to echo the same sentiments regarding the 135i being a better drive but offset it with the audi being the better all rounder. Of 4 people I've asked personally, 3 said audi and 1 the bmw.
Regarding the spec, I've been given this brief list but they can get the full list from audi on request. Would the below include some things you mentioned.
Specification -
• Audi MMI System
• Bang & Olufsen Premium Sound System
• Bluetooth Telephone Equipment & Music Streaming
• DAB Radio iPod - AUX, USB, Bluetooth Connectivity
• Dual Climate Control Air Conditioning
• Flat Bottom Multifunction Leather Steering Wheel
• Heated Seats
• Full Black & Red S3 Leather Interior
• Cruise Control
• Automatic Wipers
• 6 Airbags - Drivers, Passengers, Full Side Curtain
• Rear Window Privacy
• Electric Folding Wing Mirrors
• Parking Sensors - Front & Rear Screen Display
• 18" Titanium Alloy Wheels
• Heated Door Mirrors
• Hill-start Assist Control
• Auto Dimming Rear View Mirror
• Black Edition S3 Body Kit - Brakes, Suspension and Exhaust Package
• Remote Central Locking
• Alarm Immobiliser
• Automatic Xenon Headlights and LED Day Running Lights
The only thing I’d say if you go for a pre-facelift I’d get the tech pack as you get a larger central screen which looks less dated and personally Super Sport Seats are a must for the type of car.
I think your best bet is probably YouTube for exhaust clips or maybe some members on here might be able to share. 66 reg models have swooping indicators, they may be more expensive but if you are financing the car you may be surprised at the figures between the two as the newer car should have a higher residual value.
I have a feel the seats you refer too are not in this car I've been looking at. Would I be correct in saying the sss are the ones with diamond stitching on the corners? They look unreal I must say and I think the tech pack is included but would need to ask further questions with regard to this.