- I would like to try out the dual wielding options. That was the first reason why I discovered the classes.
Definitely the Stalker. Rangers get free proficiencies in Dual-Wielding.
- I want the character to have a good or average AC
Swashbuckler has great natural AC.
- I want the character to be versatile, so that he also can use bow with a certain skill
If you are going for Bows the Ranger would be the obvious choice. There are some nice Short Bows in the game but a cool Longbow outdoes them at any time.
- I want the character to be able to deal out good (or better 
) or average damage.
Both can do that. The Stalker can (ironically the Swashbuckler/Thief can't) backstab which will kill some annoying folks in one blow.
All in all I'd vote for the Stalker for several reasons
a.) Backstabbing
b.) Longbows
c.) Natural Enemies. If you e.g. choose Trolls these normally annoyingly strong fiends will fall like flies.
d.) Stronghold quests are more interesting
e.) Priest spells
In ToB the Swashbuckler may eventually outgrow the Stalker on higher levels but as SoA is the longest and most fun part I'd go for the Stalker.