I don't play Skywars a lot but I thought I'd go with some creative picking in this, probably some unexpected choices.
Favourites:
Trees - All player islands are flat, they all have an equal amount of chests and the distance between them is super small. I feel like this map gives all players an equal fair game no matter what island you choose. But I do feel that center is too far away, it should be that players are fighting over center not that the first guy there gets it and that's it.
End - End is the only map that has Chorus fruit and this essentially changes many aspects of the game, makes it stupidly more fun. End also has islands that are very close to each other plus the addition of islands that fill the space of the player islands and center, making sure that players don't have to bridge for 20 years to reach mid.
Desert - Another version of tree's without the tree's on the islands, it's perfect. The distance from mid to player islands is fair and the islands are fairly close together and they're pretty flat. Love it.
Dislikes:
Beach - I'm completely OK with the islands being connected, but why do you have to hide one of the chests in the parasol, it's not just hidden, it's actually pretty hard to get into. By time you've gotten into that chest some guy has probably rushed you and killed you. The map also has so few chests and the center of the map is a deathtrap and an easy kill farm for someone with a knockback enchantment, this is because the middle is essentially a sand island with this dumb clay structure that only allows players to hide on top of it or run around the outside of the ring making them a perfect target to be shot off.
Sundae - One of the two chests is on the side of the island, it's almost impossible to open quickly without being a ripe target to be shot off, this map is so stupidly hard to manoeuvre in, I can't get from here to there without using blocks, the islands are way too small and the center of the map is way too far away. You can't have the islands that close together and make them that small, that just allows players to hit each other off, no proper pvping actually happens on this map.
Tron - This map is so ripe for camping, one guy that's in center can easily block himself a safety support and you'll have a stupidly hard time getting to him, most of the time it doesn't even classify as proper camping. I also hate the placement of the mid chests, they're all over the place, if you're skilled enough to get to mid without dying you'll probably never get more than two chests before you die because they're so far apart. I also have to stress the importance of adding a hollow island, on this map there's nowhere to hide if you're getting shot at, the only thing you can do is place a block wall. This map would essentially be like Trees if it weren't for this fact. You could also massively improve this map by adding ladders to the tree's the same way that Rainbow does because all of the pvping on this map happens on the exact same layer.
Nether - I genuinely don't know what mid is supposed to be and by god is it far too big, how am I supposed to navigate that and find people without being shot off? can I also emphasise my hatred for lava, I know this is based on The Nether but at least put stained glass instead of real lava or put extra lava buckets in the chests or something. I'm sick of falling in lava and never being able to get out because of one player.
Dinosaur - Everything about this map is perfect apart from the center, every single game there is always that one team that stays on top of the volcano, I think that the volcano should be reduced in size or add lava to the top of it so that players can't really get up there without some form of effort because it's ripe for easy camping and it's difficult to get up there.
Music - Not only is mid blocked by useless obstacles which are essentially there for decoration but the top of the music box isn't even equal to the height of the islands, you start bridging and you miraculously make it to mid but then you just hit a wood/wool wall and then you have to nerd pole about 8 blocks to reach the top. This puts you in a stale position where you have to be out in the open and you can't move, making you ripe for shots because you have to pole upwards to get onto this music box to get the mid chests, furthermore when to get into the box you have to break the top and fall in then take fall damage, you then have to nerd pole to get back out and it's also COMPLETELY flat on the top so when you get onto the island you can also be easily shot off. This map is a complete deathtrap and an easy deathmatch for bow spammers.