Bash has a very barbarian feel to it. You could always just rename Bash to Slam and call it a day, but I had some other more flavorful ideas.
Whirlwind or something to that effect. Basically an ability that would let you tag all the mobs in a room with damage. It would do at least 50% reduced damage maybe more like 75%, but it could trigger multihits so you could have a chance to proc special hits like lethals. Downside would be shredding the Hell out of your weapon. But it would be intended to be aggro generating ability for room tanking. Basically let you tag multiple mobs at once and put damage on everything so it turns to you. You wouldnt want to make it something too strong that people would spam it over attacking but I wouldnt put a huge cooldown on it. Maybe 20 sec. I don’t know what logistical problems something like that might cause on the coding end tho lol.
Sundering strike. A devastating blow struck with precision to slice thru enemy defences, lowering its armor by 25% and doing a fat chunk of damage and drawing aggro. Could maybe only be used on enemies before you gained aggro, kind of like old bash. Would be good group utility too.
Stances could be interesting, but if your replacing bash may want something more active. But being able to switch to battle stance to increase damage while in small parties or go defensive in big parties could be cool. Maybe a 5-10% bonus for battle that also increases accuracy by 3% or something and a 5-10% mitigation for defensive and ups your shield block value…
If you end up doing the two hander/dual wield idea, battle stance plus that could make a fighter bring some ok damage to a party if he needed to play more of a dps role.
Or going off the twohand idea again you could have three individual abilities based on what you were doing. You could maybe Shield Slam if your using a shield and it does damage based on block value and nice stun, Cleave with a two hander, just a big attack on a seperate cooldown from your attack timer that you can use periodically, and Quickstrike, kinda the same thing but for dual wield.