The Deathbringer's Will is actually pretty bad for cat druids. Realistically the BiS trinket setup will be 258 Death's Choice/Verdict (silly alliance) and Herkuml War Token (from badges).
The reason why the Deathbringer's Will is bad for Ferals is because of the ArP proc. Cat Druids are already pushing past the soft cap with ease and this trinket, while the passive armor penetration is great, is almost useless 33% of the time already. Now tack on the fact that another proc is 600 strength. This is bad. There's no real way around that. The only proc that endures for us is the Agility proc. 1/3rd of the procs being good for us means that this trinket is best left to classes such as rogues and DKs who can use each proc.
Get one of the deaths choices and the badge trinket and you'll be golden. Until then Greatness/Badge Trinket or Death Choice/Greatness is better than using this trinket if you're already sitting above soft cap. Again, even if you're below the soft cap with this trinket, it's best left for classes who will be able to use this trinket as BiS or close-to BiS.