I've never been super keen on the idea of remakes, so I voted for none. However, if I did have to choose, I'd probably go for Zelda II. There are so many things they can do to improve this game. It's definitely the black sheep of the series, which is a shame because even if it is ridiculously hard and I've never come even close to beating it, I know that it is a good game if you can get around the difficulty, with many things contributing to its overall decent quality.
For one thing, it has a massive world, arguably the biggest in the series (to put it into perspective, the entire world of The Legend of Zelda fits into just a small corner of this map). If they were to remake the game, I would want it to be a 3D game, or pseudo-3D kinda like ALBW. Side scrolling doesn't really work for Zelda. I can see Zelda II being a fantastic game if it is done with either a top-down or behind-the-back perspective. They could totally change the gameplay of the game while still keeping the large overworld, dungeons, towns, enemies, story, etc. Remove the side-scrolling aspect, improve the graphics immensely, improve NPC dialogue and make character interactions more interesting, make the plot more clear, make the game longer, etc, all the while keeping it as the same game. It's totally doable and it has the potential to be an incredible game.
I don't see this happening anytime soon though, which is alright, it's not a necessity. Would definitely be cool though.