I bought an AX 1.4 diesel (Debut model) new in June 1994 - first new car I had ever owned. I was looking for a small economical car which would transport me from Kent to Berkshire every day on a long motorway commute.
Over the ten years I have owned the car, I've had very few big problems (usual consumables are easy to get hold of and relatively cheap). The main unusual problem I had was the boot lid hinges snapping (three sets of replacement hinges requiring welding in position on a thin part of the bodyshell!)
More recently, the alternator failed (but it was 8 years old and there was about 140,000 miles on the clock!)
In short, the car has been excellent and has never let me down in a decade of being thrashed along the outside lane of the motorway. This may have been partly down to sticking religiously to the 6,000 mile service intervals (which these days is quite a short interval). I also found that the car was very comfortable - unexpected, but then I never travelled in the back seats which are probably not all that!
Recently, I have replaced it, but with a Renault. It probably would have been another Citroen, but I was stunned by the appalling service I received from my local dealer. I was refused a test drive despite having made an appointment because they had "sold the demonstrator" and was then told "I'm afraid we can't let you test drive a car on the forecourt". No reason was given for this, and despite assurances, they never contacted me to inform me when the new demonstrator was available.
Still, I have fond memories of the AX, and was genuinely sad to part with it.