First of all to becone good is sticking to a class, play on highrating and gain tons of game experience. If then you want to reroll you should first read the whole spellbook from race passives till class passives (ye no joke), reading guides and watching videos or best, spectate good people on pandawow during arena.
So ye only chance to become better is to que against good people. So you are forced to play with randoms unless ur friends are pretty good
That are my tips to reroll in general.
Otherwise yeah, if you tried already every class and nothing makes fun theres no reason to continue playing lol ... just get the class where uve the most fun and which is viable in 2s since you wont be able to practise in 3s on Pandawow due no queues nor good teams.
For my part, im playing like 9 different classes and so also their different specs. Cant complain sbout game fun :D