Depends what u are doing these cs games for...exp? mf? both? If for mf, then u do NOT want to play single player. Two person is best. And 8 person always best for exp. If u are in an 8 person game and dont party, u dont get the 35% exp bonus that goes along with it.
I've seen bone necros who can move fairly steadily, in an 8 person game, mostly alone, thru the river into the cs. They usually use bspirits to make the first few corpses and then summon as a meatshield and use them for CE. Pure poison necros have problems in the river, because Maggot mothers and MawFiends are poison immune. But little maggots arent with LowRes curse and that can be used with CE to blow up nearby pimmunes. Trouble is there will be some survivors, and u may want to use terror or one of the skills from that subtree to bypass them and get into the CS - where there are NO pimmunes. It's very hard to go full pnova synergy AND a good lvl of LR curse AND have some summons that can do decent damage with decent life AND then to develop an effective bspirit/spear. So u have to make some minor compromises.
WW barbs can get thru the cs, even with one pt in berserk. But there is a painful way to do it and a smartbarb way to do it. Solo, u are going to want to use some taunt, to steer mobs away from the mages to avoid IM. This takes TIME. Even when u have a mage alone, and go up to him and hit him once with a berserk to check that u are out of IM range, he may move away from u and cast IM while u are starting ur WW = splat, dead barb. U must use a decent lvl of warcry if u intend to kill mages. Oh, u can bora ur way to the seals, leaving everything unkilled and try to berserk the seal bosses - that is very difficult to do, even with howl (which wont work btw if u arent at least lvl 80). There will be multiple mages and even if u can howl the entire mob across the cs, the mages will not budge and while u are ww'ing one of them, sooner or later u will get IM cast on u=splat. Howling items on ur person such as rcage have some use.
If u are doing this mostly for exp, then choosing the ww barb route can be very painful, ESPECIALLY solo in 8 person game, unless u follow a ruthless protocol of survival in the cs.
Lightning zons have terrible time with lightning immunes, such as storm casters. These drain their mana making it hard for them to kill anything.
Dual and tri elemental sorcies can do the job, but I am strongly in favor of mid lvl static to lower the hitpoints of most of the monsters on the screen, and not depend on a few +skills to get the job done. High lvl static means u can cast it 1-2 times before ANY monsters can even hit u, which will encroach on ur mana supply if u are using the mana shield. Just a dozen total points in static can allow u to get high lvls of fire/cold skills, then u are tri-elemental.
Static and CE are the most damaging skills in the game, and each require less than a dozen points (then with +skills will extend it even further) to reach near full fruition! Neither require much prereq skill pts.