That certainly makes it sound like Lan is the best. If no one else is able to top Rand (apparently before he lost his hand) besides Lan, it certainly implies that Lan is the top dog. I assume that this is referring to Rand sometime after he lost to Riatin, but before he lost his hand.

However, things have changed since then - the text in TGS certainly makes Gawyn out to be an extraordinary swordsman. The thing that makes me think that he might be able to take on Lan is the simple fact that BSand used the plot device of Lan as a reference point to indicate how talented Gawyn is. Lan lost a third of his matches against the dude (for some reason, I can't recall his name. I think it was 'Sleete' or something, but that doesn't sound right somehow). Two in seven is practically the same as one in three. As I recall, Gawyn fought three or so matches against two warders at once, and won every time. The numbers say that Gawyn is better than Lan. There are other factors that come into play as well though. For example, Lan may not have been at the peak of his skill when he was still sparring with the Warders.

It's hard to tell, IMO. If I had to lean one way or another, I'd call it for Gawyn. I'm more inclined to think that Lan's skill has started to decrease with age, but that is something we can only speculate about.