Long weapons get the first strike in the first round, but afterwards the shortest weapons strike first.I've said this before. And then at other times, I've said I'd go with "highest Dex goes first" (Holmes initiative.) The problem is, I like both, and I can't decide whether weapon length should trump Dex, or Dex should trump weapon length. So maybe a mixed approach is in order?
Highest Dex gets first strike. On the first round of combat, or after withdrawing and then closing again, you can use triple your weapon length in place of your Dex, if you want. Afterwards, you get to add your opponent's weapon length to your Dex if your weapon is shorter.
And for the record: if you are performing a mental activity, like casting a spell, use the higher of Int or Dex. The spell level is treated as your weapon length, if trying to cast a spell in combat.