Probably the first game. It was easy to get "lost", but it was also the easiest to just play, and get into, without over-complicating things. My fav. is Link's Awakening, and it's a good game that's easy to get into, so I'd say that one as well.

Well if you liked Spirit Tracks, try Phantom Hourglass. I found that to be the better game overall (if you ignore the temple of the ocean king).

The newest 3DS zelda is quite a good entry point as well. Not much story or any kind of baggage, just really great gameplay.

if OOT does not tickle your fancy then you are out of luck with Zelda games.

Wind Waker and Skyward Sword actually sound like the 3D Zeldas you may like the most.

But I think there's a bit too much of a focus on trying to redeem your love of 3D Zelda since OoT didn't kindle the flame. You liked Spirit Tracks. Try another top down Zelda! They do feel different from the 3D ones, and with the exception of perhaps some portions of Skyward Sword the 2D pacing is always much higher with the worlds more "crowded" than the 3D ones.

If Spirit Tracks was your jam I think you'd do well with Minish Cap, that's a load of fun and you can play it on your DS. It's often overlooked for more noteable titles but it has great charm and gameplay. Finding a cartridge under $20 is hard though.

You have a 3DS though. You've got great 2D Zelda experiences available right there on the eshop! The original is $5, Link's Awakening DX and the Oracles are $6 apiece (if you buy one Oracle and like it then buy the next one and play it too. They should be played together if you enjoy them.)
And of course A Link Between Worlds. Since you're not actually a newbie to Zelda I think this would be a good game to continue on to.

I'd take one of the cheap top down options if I was just looking to further test my interest in the series. Link's Awakening probably.

That's not always the case though! I am not that big of an OoT fan, yet I can easily enjoy other Zelda games like Majora's Mask and Wind Waker!

What specifically about Ocarina of Time didn't click with you?

Dungeon design. I have no real clue why, but I just dislike the way the dungeons are in that game. In contrary to Spirit Tracks, because I did really enjoy that game. I like the overworld for both games though.

Tie between Wind Waker and Skyward Sword for me. Ocarina of Time was pretty dull for me as well, don't feel bad.

Wind Waker might be good for you, as far as console entries go. I haven't finished it myself (I had to borrow a copy to play), but I got a few dungeons in, and it has a very different feel from OoT. Also, while I haven't played it myself, you might look into Twilight Princess. Failing that, since a 2D Zelda clicked with you, that might be another option to pursue.

Whatever you decide, Majora's Mask and Skyward Sword are probably not good for you. Majora's Mask is obviously very similar to OoT, and Skyward Sword just isn't very good.