DW Rogue Assassin is my favorite so far, but admittedly I've only played in like, 3 classes for more than just an hour or two: DW Rogue, Archer Rogue, 2-handed warrior.
2-Handed warrior is a challenge for sure, but it's clunky, and in many ways inferior to S&S among other classes. If they fixed the bugged detonations, made block and slash less clunky and stamina thirsty (I wouldn't mind dealing less damage for costing less stamina...) then it might be more worth playing. Reaver+2H does loads of damage, it's nice to do 1000+ damage with every attack at like level 12, but then you realize that the gameplay is very simple, walk up to enemy, attack 3-4 times with dragon rage, then devour, rinse and repeat, no flanking or positioning needed (unlike DW rogue).
Archer just isn't my thing. It's strong as heck, feels like playing the game on easy mode, especially if you have like, S&S warrior tank and 2 mages or mage+archer for a party. It is however, nice to be able to attack without frustratingly have my attacks/abilities miss due to terrain or something stupid like that.
DW Rogue just hit the spot for me, especially after level 12 or so. Early on its kinda miserable, barely do more damage than a warrior even when flanking, and still are super squishy and melee. However once you get decent gear it's pretty fun. I really liked assassin too mainly for it's stealth interactions, i.e. refresh stealth cooldown on kill and auto crit for first attack out of stealth. The hidden blades and mark of death are definitely strong, but obviously not that interactive or fun. Useful for boss/lieutenant fights though for sure.It's just fun darting around in and out of stealth though.
Next playthrough will definitely be a mage. Probably all-out DPS mage, rush down fire and lightning tress for fire mine and then static cage for maximum damage potential, then probably spec out as a rift mage for the mana regen+quasi-singularity for aoe damage combos. I'll probably take Dorian, Varric, and Cassandra as a party, maybe Iron Bull respecced as a S&S tank.