Defense
First, don't even bother with defense unless you are a defense-based toon (VEAT, SR, Shield, Ice Armor, EA.) I believe most people would suggest to slot for at least 55 defense to a given position/type (ranged/melee or S/L being the most common) in order to be somewhat effective in PVP. SR scrappers can get the highest values of defense with elude, but even then it is cut in half by DR. Typically a DR'd SR running elude will be sitting around 52-55% in PVP (which is around 115% non DR'd.)
I know a little bit of defense wont help much but after a point defense becomes very tough but i dont know how high that defense has to be to reach that point and how high it has to be in pvp and pve so i can make builds on mid because it doesn't count in DR