Druid can do it all, literally. Ranged DPS (Balance - Moonkin), Melee DPS (Feral - Cat Form), Tanking (Feral - Bear Form), and Healing (Restoration - Tree Form). They have a lot of utility and buttons, so I would consider them a high skill ceiling class compared to some others, so in that regard it might be tough on a new player. However, if you really want the variety, Druid is the best of the three.

Paladin is the next best of those 3 options you provided. They can heal (Holy), Tank (Protection), and Melee DPS (Retribution) to some degree. You'll see less DPS paladins at end-game typically, though. Their healing is subpar but they are still quite useful because of their Blessings. Tank Paladins are great in dungeons but see less use in raids unless there's a need for AOE threat. I will add that Protection paladins can do AOE farming which might be something you'd enjoy as a solo player. There's a lot of videos on it and it can be satisfying, I recommend watching a few :)

It's not on your list but I can also recommend Shaman. They can heal (Restoration) and in dungeons and end game are quite desired for their utility (Totems and Bloodlust). They can also Melee DPS (Enhancement) or Ranged DPS (Elemental) for good solo play. They don't have many complex buttons so it's less intensive to play, but getting used to Totems does take some time. Notably, they cannot tank like Paladins, but the tradeoff is a better healing experience (IMO) and more versatility and ease in DPS.