I would say samurai

The samurai. The equipment is better, the katana was the sharpest thing on the market when we're talking swords here. The skills were predominantly better (not that the knights sucked but still). And so the samurai would win lol

A Samurai. The Medieval Knights armour made it very difficult for him to maneuvre and quite easy to remove from his horse.

I say Knights, many think their armuor is stiff but really is flexable and they can even do cartwheel's in it, They are also bigger and stonger to so I do say Knights

The training regimens of knights and Samurai were very similar. Both were experts in armed and unarmed combat, both in and out of armour. So if it comes down to a duel between an unarmoured knight and an unarmoured Samurai, it comes down to who's the better fighter that day. It's impossible to tell, since both were experts at duelling in such a fashion. Withing knightly circles, unarmoured longsword duelling was considered the pinnacle of swordsmanship, since there is no room for error. Where the knight comes out on top is technology. Assuming that the combat takes place with full armour with swords, the knight has a significant advantage. European plate armour is simply impervious to cutting blows from a sword... ANY sword. The katana is an excellent weapon, but it is still just a sword, and is actually more fragile than the European longsword. The katana's legendary cutting ability is just that: legend. It's a very fine two-handed sabre, but is prone to breakage in reality. One can see historical katanas that had the ends snapped off and were since repaired. It is certainly not capable of damaging plate armour in a cutting fashion. European longswords however, are not prone to breakage and are incredibly resilient. Europe had better ore than Japan, resulting in superior steel. Even so, swords of any kind are not good against armour when used in a cutting fashion. Both fighters would likely go to half-sword grips and try to find the gaps in the armour using the sword as a short spear. One finds these techniques both in medieval fencing texts and koryu (classical) kenjutsu. Since the knight's armour has better coverage, that's a large advantage. The idea that knight's armour is more encumbering than Samurai's armour is again, a myth. Both European and Japanese armour weighed in at about 60 lbs for a full suit, much less than the full kit of a modern infantryman. One can do a cartwheel in full armour. Remeber that a knight was required to be able to vault onto his horse in full armour without the use of stirrups as part of his knighting. In the end, it's pointless question. It's like saying who would win, a knight from Burgundy or a knight from Saxony? Or a Samurai from Prefecture A vs. one from Prefecture B? Both the knight and Samurai were elite feudal warriors trained in similar martial arts from a very young age. It comes down to who's the best and luckiest fighter on that day between to individuals. Whether one is a knight or Samurai really doesn't matter.