To learn to pk you want to have a class with which you can hunt without being worried all the time (at least that was what did it for me).

Three classes achieve that easily (already at low- and mid- level):
- assassin: You will feel like a predator since you can decide when to attack and do not have to worry about people attacking you if they cannot see you. You can see all but rangers. You can choose chaotic evil and attack all you think you can kill. Very round, nice class also at hero.
- ranger: similar as assassin but you are limited to wilderness which is a handicap. On the other hand, chaotic evil allows that later in life you give up coins and join outlander.
- thief: similar as above but very weak at hero if you do not know preps/gear

All those are hiding classes and their usefulness in hero exploring is bellow average.

In addition since those are hiding classes, making friends will be harder. Even if you have friends they will sometimes not be able to call you on an expedition if they can't see you.

If that hero level exploration is your focus I would choose a class that is desired in such groups.

- bard: excellent choice if your focus is on exploring
- shifter: defensive, offensive, or utility or any combination thereof. If you are very new than an offensive role is easier to fullfill since in emergiencies you do not need to decide on anything just follow.
- healer, paladin: also great choices
- warrior: swords are (in my opinion and to my big regret) the strongest overall spec

Cabal choice:

You have to decide whether you want to join as early as possible or join late and focus on other things before that.

If you want to concentrate on exploring and what not and just have the option of joining at hero once you get bored nexus, fort, tribunal, and outlander are all possible choices. (For later joining Nexus or Fort you do not need to restrict yourself at all, for tribunal you should avoid commiting crimes but that is no biggie for an exploration based character, for outlander you need to spend time in the wilds which is not hard - coins you can always give up later.) I would not recommend empire as a cabal to join at hero although I did it once myself. (If you are uncaballed and kill the emperor a few times you will be asked to join - even if you are a class that cannot join normally and neutral evil... but if you are new joining early has the advantage that you will slowly rise in the ranks as long as you do not do anything stupid. Also, if you are uncaballed for a long time, you may make enemies in the cabal and joining later will be complicated.)

Joining a cabal early is attractive since you will immediately a group of people you can ask for info, help and what not.

However, out-of-cabal friends are also crucial given the small player base.

If you join early, nexus IMHO is a bad choice. The reason is that making out-of-cabal friends is hard since you will have to attack their cabal occasionally.

I would go fortress or neutral tribunal (or herald if you like them). As fort you can be friends with every good and neutral. As neutral tribunal you can be friendly with everybody but outlander.

In both cases, if you are a class that is good for exploration like a bard say a lot of people will ask you to come with them on interesting trips and you will see things that you have never seen before. :-)