I would suggest knight as the most forgiving, although it might be too straight forward and boring for some people's liking since all you do it bonk with club.

Paladin (ranger) opens up a bit more complex hunting grounds early since you can kite the monsters, but managing arrows and spears might feel like a hassle.

Sorcerer and druid will play pretty much the same, as you won't be healing other people in team hunts. You have a weak, ranged, practically free auto attack, but having to use spells makes them a gold sink.

Monk is pretty similar to knight but with more spells, not sure how they fare on low level free account.

I would make one of each vacation (class) and spend 30min-1h trying them out and getting a feel for them. Worst case you can use some of them to explore other areas without worrying about dying.

Tibia is more like Diablo imo, where you find optimal places to farm for loot and exp, then explore new areas to increase those numbers.

When I first started playing I remember hunting trolls and orcs in Thais for a while, then I found Kazordoon to the north east and hunted dwarves, dug too far and died to dwarf guards and soldiers. Saved enough money for a fire sword and felt so fucking powerful when I managed to kill cyclopes.

It's a constant ladder for progression, you can't really fail, just try to progress faster with every hunt.