3M was generally considered to be the best, before Imation took over manufacturing after 1996. I doubt that 15+ year old NOS disks will still be reliable (and easy to find), given that the shelf life of disks is generally about 3 years tops.

In my region, Maxell is still spinning out new floppies, and they can still be found at Staples, and Office Depot. I'm not sure what the situation is in Europe, but I've never run into a problem with Maxell floppies. Their recent VHS tapes, however, are a different story.