This is different than just "Heroes That are Mechanically the Best" or "Most Superior."
I'm wondering which heroes you simply like playing the best, regardless of their overall effectiveness and utility. This could be because you like their artwork, you like the characters from the source material, or just because they produce a type of playstyle that's appealing to you.
For me, simply put, it's Elladan and Elrohir.
Mechanically, they're good, though hardly "optimal" for building the most powerful decks in the game. But there's just something about being able to "break" the action economy right out of the gate, both for attack and defense that appeals to me.
As a game player, I've always favored "well-rounded" approaches to games. In RPGs, for example, I'm the type of player that has to dabble in everything; I never want to specialize, or feel like I'm "trapped" in a niche. The thing about Elladan and Elrohir, is that you can fit them into different playstyles very easily simply by swapping the third hero, and adjusting the allies / attachments in your deck to fit a need or theme.
The weakness, obviously, is that you're pretty much forced to run them as a tri-sphere, which can be hard, and limits some deck building options.
But I've just found I really enjoy playing with them---Rivendell Blade for Elladan, Dunedain Warning for Elrohir, along with the Dunedain and Rivendell allies. My most common tag-along is Lore Aragorn, for versatility.
They're usable with all of the Noldor-trait cards too, and other than in the dedicated Gondor quests, are almost always thematically appropriate. In the fiction of Tolkien, seeing the twins in Erebor, or Moria, or Mirkwood, or Lothlorien, wouldn't be a strange sight.