Depends on what you're doing. My default is Skullders unless I have a specific need. A javazon really benifits from +skills, more than most melee builds anyway. Most go with any 500+ light/med armor for a rune word base. Arch plate is a common one.
Like Shags says it depends on what you plan to do with her.
I'd go with either CoH or Enigma. Both have +2 skills. One has resists, the other teleport. So it depends on what you need most. For CoH i'd go with archon plate, for enigma a breast plate (though i see many enigma mage plates too).
Or if you're gonna go MFing skullders would work too.
The rational behind using a BP is that it really doesn't matter what defense is on an armor that doesn't pump defense high enough to matter. People use the armor that has the lowest requirements rather than the highest defense for Enigma since it has no +%defence. Don't make the mistake of using superior armor as this will just raise the repair costs.