I can only help you telling you that you can check directly which impacts more using the attack value feature on your skills window (together with other stats as critical, leechs, resistances etd).
+1 attack is a fixed number which means that it will always provide the same amount of damage, while 7.5% sword skill is an scalable number which means that under certain conditions u might be getting more damage from it, I just don't know how much +1 attack impacts to melee stats sadly but u can check it yourself (and if possible share the answer)