Like FB said, if these spokes from from a very specific cause then you are probably going to be fine if you just replace these. If they are breaking because of fatigue it is probably a good idea to replace them all.

I believe in DB spokes being superior when it comes to durability but don't think you cant build a wheel that will last thousands upon thousands of miles with straight gauge spokes. If you have a nice hub/rim, sure splurge and get DB. If you are trying to keep a more inexpensive hub/rim combo going I would just use straight gauge from a quality brand like DT or Wheelsmith.