in the old days, ppl like to use longswords (pkers mostly)...
coz u have a higher chance to hit higher...
but nowadays, ppl prefer to scimmy, no matter wat... even pking...
coz they think the faster speed of scimmy can fulfill the less chance to hit high comparing to longsword...
Based on runescape provided information
D long speed = D scim = Whip = SS
Because they are all :6
so it's no difference for the speed
Just the matter of max and accurate
If you are p2p,D long will have a special which can be used four times hitting a high damage
D scimitiar will have a higher attack bonus meaning higher accuracy and higher in strength bonus which means normally hits better then d long,But the special attack is not as good as d long.