Hi Pia and Hans,
Yes, Dacron is the gold standard for cruising sail material. Built and designed well, they can serve well. And, as Brian observed, they are the easiest sail to repair in the field, often just using sticky back sailcloth or by sewing.
That said, it sounds from the sailcloth you mentioned, that you are interested in a more performance-oriented sailcloth. I have had laminated sails (jib and mainsail) and was quite happy with them for the most part. Their shape was good almost to the end. The down side was that they looked ratty fairly quickly as mold creeped into the laminate. And when they started to die (admittedly at 7-8 years), they died quickly in multiple places (think multiple organ failure) and were challenging to fix in the field.
I have also had much experience with Dacron sails and many have served me well. As said before, they are the most field repairable sail and any loft in the world (or canvas worker for that matter) can affect repair.
For me, Dacron lost sail shape a sooner than I wish. This occurs gradually and is endemic to Dacron sails exacerbated by being somewhat more unforgiving in this area of the occasional fire drills that happen to offshore boats. Now many offshore sailmakers will attempt to deal with this concern of the customers by suggesting a heavier cloth, but this is at the expense of weight and ability to adjust sail shape. And most of our sailing is done in light to moderate wind, especially if you sail in the center band of the world. So, sail shape and adjustability in these areas is important.
Depending on mileage and the number of fire drills, I started to see the sail shape of Dacron sails show signs of sail shape problems after 3 years or so and certainly by 4- 5 years. My casual observation of other boats supports this. The trouble is that the sailcloth is still good for another few years (before UV takes its toll) and most cruisers end up nursing their sails along a couple more years and tolerating the compromised sail shape.
I like to sail and I like to sail well, but am no racer. My research 4 years ago lead me to have a whole new set of sails made on HydraNet Radial sailcloth made by Dimension Polyant (sailmakers over the years have developed great sail materials over the years, but then they try to flog them exclusively in the face of often better choices elsewhere). We are in our 5th season (mostly higher latitude sailing, 6 months out a year and one Atlantic crossing) and their shape is as new.
HydraNet Radial is a woven cloth of polyester (Dacron) and Spectra so it breaths and dries which was important for UK weather where we were at the time. And it is field repairable as sewing is the way to go and the cloth does not take well to adhesives. It is impressively flexible in its construction, so sail panels can be designed to have the strength in the correct places. Please google for details and the many reviews that I am sure exist on the internet.
And come back with questions, comments etc. and let us know what your researches reveal.
My best, Dick Stevenson, s/v Alchemy