Paul,
Quite correct that it depends upon the plastic used for the line. Some lines such as the AST formulated SA lines have a lubricant built into the coating, the best way to clean these lines is with water and a micro abrasive so you have a new ready lubricated surface to cast with. Silicone such as that bottled by Snowbee tends to work well on Shakespeare made line but my Orvis lines do not like it, it makes them wear significantly faster and leads to premature cracking of the coating so I tend to use Orvis cleaner with them but this is not great on Rio lines, Rios agent X seems to work best on them, see where this is going? After a good bit of trial and error I have come to the conclusion that it is best to use the manufacturers recomended cleaner, it is only a few quid in most cases and in my experience it is usually a few quid well spent if you have already spent £50+ on a line. Would be nice if all manufacturers of top end lines followed the example set by Snowbee and included a bottle of dressing with the line it cost peanuts.
On the subject of lines, Mike kindly lent me a line over the weekend to try on a rod I had previously not been that sure about, had tried it with TTs Wonderlines & various SA offerings without sucess, what a difference
Cheers
Ben