Before I looked at your attachment, the compare/contrast ideas that sprang to my mind were the similarities in how the verse is written: They both use alliteration--repetition of (usually) consonant sounds three or four times per line--instead of rhyming)*; a difference is that Gawain stanzas end with a "bob and wheel," the short two-syllable line followed by four short lines, while Beowulf does not. Also, Beowulf bridged the transition from the old Anglo-Saxon superstitions and religions to Christianity while Sir Gawain's religious backdrop was Christianity only.
* Example from Sir Gawain:
Reckoning of the Round Table all the rich brethren,
with right ripe revel and reckless mirth.
And an example from Beowulf:
Swore by his sword, and young men swelled....
(A lot of Beowulf translations don't preserve the alliteration, though. Too bad, because it's cool.)
But to the bits you're asking about:
Appearance of halls:
- Hrothgar's hall is huge, "a hall that would hold his mighty / Band and reach higher toward Heaven than anything / That had ever been known to the sons of men." It's strangely reminiscent of Solomon's wealth, which is described as having "surpassed all the kings of the earth in riches." Hrothgar's hall is also adorned by orders for work sent to all peoples, suggesting that it has samples of the art of various cultures all around (this bit is from the Seamus Heaney version, but doesn't necessarily appear in all versions).
- King Arthur's hall is also immense. It's large enough for all the court--and we're led to believe there were huge numbers of lords and ladies and knights--as well as tons of food and bands and players. It's also large enough for the green knight, himself described as huge, to ride in upright on horseback. Arthur's hall is richly adorned, as well. Queen Guenevere is
Seated on the upper level, adorned all about;
Fine silk surrounding her, a canopy overhead
Of costly French fabric, silk carpets underfoot
That were embroidered and studded with the finest gems
That money could buy at the highest price
- Hrothgar: In the short reading assigned here, the only entertainment mentioned is that he dispensed riches to his subjects (72). If you read ahead a bit through line 90, though, you will see that he also has poets and singers and great feasts with happiness and merry-making loud enough to wake the beast Grendel.
- Arthur: "Rich revelry and carefree amusement" (40); tournaments and jousts (41-2); "dancing and song" (43); feasting and merry-making (45); dancing (47); Christmas service in the chapel (63); exchange of gifts (66-70); and Arthur himself will not eat until someone tells him "a curious tale" or he sees a good joust (93, 96-7).
Who was present/absent:
- Hrothgar: All we're told in this tiny bit of Beowulf is that the hall is open to "old and young," to whom Hrothgar gives out treasures to reward them for their bravery in battle. This could include women, but wouldn't include children. His company wasn't limited to nobles and lords, clearly; the bounty and the honor here went to the brave and valiant.
- Arthur: The hall is peopled by the lords and ladies of the court and his knights, as well as the necessary servers and performers. The image is of the the rich and beautiful, as well as the men who were brave and skilled enough to become members of his Round Table (39).
- Hrothgar: Festive, clearly. He hands out rich gifts to all who have earned them, but there's also (as I mentioned before) a great uproar from the feasting and merry-making, which suggests happiness, music, dancing, and laughter.
- Arthur: Mostly festive and joyful (48), but also pious (as they finish their Christmas worship and leave the chapel). Like Hrothgar's mead-hall, Arthur's is a din of merry-making and feasting.