Let me go over the Zelda games I've played for 2D;
Zelda 1: Great game, aged poorly but is still pretty cool. Set the pace for later games well.
Zelda II; I love the game, but I suck at it. I still find it very fun and unique.
ALTTP: Nice game, and feels fair challenge-wise.
LA: Like, my favorite 2D game by far. Amazing gameplay(especially the original). Haven't started the remake yet. DX version is... okay. I prefer keeping my Rooster, thanks.
Oracle Games: Amazing games and aged very very well. Just get the original copies cause the 3DS downloads fail to give you the hidden shops. If you don't care about 100% completion, though... or you could use passwords online?
The Minish Cap: Awesome game. Basically akin to ALTTP in many way, but feels a bit more balanced. Only one boss felt difficult, imo.
ALTTP/Four Swords: Quite a few changes, and feels far better. Four Swords bit is a nice smaller game to play in.
CD-i games: Haven't played them, can't say, but will note that the sidescrolling ones got mediocre reviews on release, which is saying something with how much they're hated now. Only Zelda's Adventure actually did poorly the entire time.
ALBW: Great game, though it can get a little difficult sometimes, far more than ALTTP. The item meter however is very very nice(way cooler than the stamina meter, which is... okay).
PH: Decent game, but the controls suck for sword/movement. Items are great.
ST: Haven't played yet. Won't till I beat PH.
I've played Zelda Classic(Randomizer, though was Modern version?), and it was pretty good. Very improved. Couldn't use proper controls due to keyboard only, though.