>>>I give up, which one determines how often you hit?
Neither. Only your level, offense, and weapons skill figures into the chance to hit.
STR determines max damage and average damage. Higher STR will raise your damage cap, and will also increase your likelihood of hitting closer to your max. The exception to this is Archery, where Dex determines this.
Dex determines how often a weapon will fire a random process, and also figures into critical hits for warriors. It also figures into some of the rogue skills.
-Gordon