What an incredibly well put together car, this A4 is one of my favorites. Being a long time Audi fan, I will try to be objective in this review, this is my honest experience of this car.
SE model is nothing special, but has all the electrics you could want from a 2009 car. Seats are very comfortable, and I have come to prefer them over leather in the higher spec models. Inside in general is very comfortable for all and lots of room. Dashboard is very stylish and well laid out, everything is at hand, ergonomics are perfect for me at average height and weight. A common complaint, but the electronic handbrake I don't like (took months to get used to), but is no big deal once you are used to it - but I do much prefer a mechanical lever.
Outside the car is very stylish in white, which is a popular color but not as common as silver. I like the look of the original alloy wheels and have made no modifications to this car. I like the shape of the A4 and the car to this day is very similar still to the shape of the car when it came out in 1995/1996 to replace the Audi 80. I had an 80 previous to this car and this car obliviously feels generations ahead, but I did love my Audi 80 (a 1992 car which yes I was using up till as recent as 2017!) and it was that car that made me finally move on to buy this one. I doubt this A4 will last as long as my 80, due to being modern and will likely get complex and expensive to repair as the years go on, but if I get another 5 years or so out of this car I will be happy.
To drive the 1.8 "TFSI" petrol is the one to have - arguably better than the diesel due to being quieter, more refined, and less complicated so no big diesel repair bills. You can also average 40 MPG if you take it slow, not exactly great (especially with the current cost of fuel!) as the diesels can do 50 MPG +, but are more expensive to repair. So factor that in with long term costs and it's really all the same. With nearly 160 BHP on tap the car is fun to drive with the 6 speed manual.
Overall this is a well designed car. Its main rivals are the BMW 3 series and Mercedes C Class. Having driven those cars I can honestly say there is little between any of them now; it just depends what you prefer, all are good cars.
Just be aware though at the age and mileage a 10 year old one might be cheap enough to buy, but do your research and make sure you have a good local independent garage to help you out and keep costs down if things go wrong, I will admit I have been lucky to have that and get such a looked after car, a lot of people will not be so lucky - there are a lot of rough example high mileage used cars out there in the UK market right now for silly prices, that will likely cost someone who does not know any better a fortune if things go wrong.