oldzmann

I traded in my A5, S-line 10 days ago for a new S4 with the 18" wheels on it. I too am thinking about getting a set of 19" as I think the car looks better with the 19's. The ride is better on the crappy roads with the 18's, but the handling was a bit better with the 19's on my old A5.
So far I like the BBS and Hartmann wheels. Although the A4 prestige S-line wheels and OEM potato peeler wheels have grown on me. Hmmmm...

troposphere

At this point get your self some BBS 20"s.
Keep the 18"s for snows if you must.

Pillbox

Ah, I'm happy to learn that you're doing fine with 19' in Montreal. I just got my S4 2 weeks ago on 18' and winter tires and I'm anxious to put it on the 19' next summer...I'm afraid the ride will be too harsh.

Barrels41

The 19"s are OK. Frankly my 17" winter tires ride allot better in bumpy NY metro. Blow a summer UHP 19" it is $350.00 a tire. 18" are a good compromise. 20" makes me nervous. Not for the northeast.

waffles

I prefer 18s, if you want winters or want to track your car you have more of a tire selection

18s are cheaper and I live in an area with a lot of potholes

Also what you will probably want to do, if you end up with the crappy pirellis or contis, is remove them and get a set of Michelin pilot sports or super sports. Put the pirellis in storage. When it's time to sell the car or trade t in, put them back on. You won't be wanting to turn in your nice tires