Daggers lower attack speed less than katars. Of course you have to take potions into consideration. In the end, people will use the potions to increase their efficiency while fighting.
Sniper 99/70 aspd with bow and no other equips (All sniper buffs and awake potion included): 182.32
Stalker 99/70 aspd with dagger and no other equips (Stalker passive bonuses / berserk potion included): 182.00
Assassin Cross 99/70 aspd with katar and no other equips (Assassin Cross passive bonuses / EDP potion included): 182.56
Both Sniper and Stalker will end up with 182 aspd in this case. Also, a sniper would get either dex or int stuff, maybe vit even, not agi. While a stalker might as well give himself agi equips, giving him 2 or 3 more aspd. The assassin cross has slightly higher aspd as you can see, only, it's using an EDP potion, and they're alot harder to get ahold of compared to awake/berserk potions. I'd say the assassin cross would end up with the best attack speed, at the highest cost, followed by the stalker, and lastly the sniper.
Source:
http://ro.doddlercon.com/calc/calcx.htmlEDIT: Forgot to mention: They're all at 99 base agi/dex.