Mind Freeze
That is unless you are on interrupt duty; then you should definitely go for 3/3 Virulence and 1/3 Epidemic instead. The loss of 4 secs on FF is rather minor compared to freeing up 3% spell hit from your gear for proper survival stats. The hit values to be spell hit capped are:
2/3 Virulence: 11% spell hit, 1126 hit rating. This equates to 9.3% melee hit which is 1.3% over the melee cap.
3/3 Virulence: 8% spell hit, 820 hit rating. This is equates to 6,8% melee hit.
0/3 or 1/3 Virulence: Don't even bother. If you are required to interrupt, go respec.