Depends on the build. I like the typical knight role so usually something like balder side sword or some type of longsword. I never used katanas on Demon's or Dark Souls, though they are undoubtedly effective. I tend to lose most to bleed buildup.
If it's just for PvE, I just use whatever I have fun with. For PvP then BSS is the closest I come to a cookie cutter build, but I do have fun with the guardian's tail. +15 it and you can't see dark moon blade on it until it swings, nobody expects to be hit for 500 damage when everyone swears that the whip sucks. I love it, just not the fact that it doesn't combo and has to be two handed for a horizontal sweep.
"invade some poor sap and jihad bomb him" - LazyKenny