So, I've been playing around with different builds in Mids for my Willpower/Kinetic Melee Tanker. I'm not expert at tanking, but seems like Willpower doesn't really specialize in any one thing. Some powersets do Defense, some do Resistance, some do Regeneration. Willpower looks competent in all, and master of none. So my question is, how to improve my slotting to best improve my tanking; for example, is it better to improve Def by 1% or Resist by %1 or Regen by 1%?
The metric I've worked out is Average Sustainable Hits:
ASH = REGEN / ( max( 100 - DEF, 5) / 100 * max( 100 - RESIST, 10) / 100 )
where REGEN is my regeneration in hit points per second, DEF is defense percentage, and RESIST is resistance percentage.
Near the bottom end, raising defense 1% is about the same as raising resistance or regeneration by 2%. Near the top end (say 40% defense, 85% resistance), 1% defense is about the same as raising resistance 1.5% or regeneration 11%. I compute the metric separately for each type of damage. The take-away seems to be resistance becomes more useful as you get closer to the top, while regeneration becomes less useful. On the other hand, there's no limit on regeneration; it's always useful.
I'm sure this is old hat for long-time Tankers, but I figured this out myself and thought I'd share. Math is fun!