Dekar vs Guy
Estpolis II tries to avoid a direct answer to this. When Dekar and Guy first meet, Dekar surprises Guy with the medieval version of a sucker punch. Guy parries successfully. The good-natured Dekar replies that the response was "pretty good" and that he's glad to meet someone who can hold his own. But Guy snipes, "If you hadn't gone easy on me, one of us could've been hurt." Dekar hesitates a moment before laughing off the remark. After that, the two become fast friends and never challenge each other again (at least not that we can see, since during the first year of Maxim's marriage I'm sure some kind of match took place).
But when it came down to asking Maxim for a one on one, Maxim's responses differed dramatically. He was willing to take on Guy, but afraid to take on Dekar. There must be a big difference between Dekar and Guy, namely that the former must be much larger and intimidating than the latter.
Too, there are the statistical differences. An unequipped level 20 Dekar is equal to or stronger than a level 30 Maxim and Guy. And Dekar is a royal knight, and would've had access to better training with a sword. Guy is a small-town hero whose skills would be less polished.
Yes, Guy is the smarter of the two, but as Dekar proves in the Tower of Sacrifice, brains don't always triumph over brawn. I think, in the end, if these two ever did spar together, it would be a draw. But if you're looking at physical strength alone, there's far more evidence in favor of Dekar being the best.