level necromancy on rogues. Shit is honestly broken, i had lohse running around bursting people while being tanky as shit thanks to boneplating and the sustain it gives.
aside from that summoning is pretty strong too, especially the lil fucker that turns into a champion at 10 summoning, bone widow is pretty good too but necromancy.
Just play on the standard difficulty (classic according to my settings), it's hard enough and you can just play however you like, no need to min max or follow strats made by someone else. You actually get to play the game for fun.
I'd also advise to sell and buy on 1 character as you can invest in barter on them and ignore it on others. And buy every resurrection scroll you see, at first you'll be scrapping for gold to get em but they end up quite cheap later on.
ALWAYS check the enemies resistances. The amount of times i've been bamboozled by that shit. The joy of having a fire mage vs a bunch of fire resistant skeletons.