Interesting question because every class is different and every new class that you don't have access to will have to be unlocked via the upper Ascension Atlas starting from a beginning class. My suggestion is that you visit the Training Room in the Research Center , and decide for yourself which class you want to play.
I use paladin but don't go for hate (tank aggro) as I use cryo and pala for solo missions. Paladin is useful when you need a tougher character.
I use lightbinder for groups.
But Pinkachu is right, practise in the Training Room.
Playing a Paladin as non-tank is pretty useless. You deal nearly no damage and you won't provide anything useful to a group. Even for solo-play nearly every other class (except supporters) are better suited for everything. (Played over 180h with pally myself)
For now unfortunately the Kinetic and the Berserker are the way to go, wich hopefully changes in future patches. But for now you are well advised getting atleast one of them.
Cheers Usche