(Good) Very effective "Stone Thrower", can shoot twice each turn. Tough to kill, able to be healed. Enemies must take Panic Tests if any casualty is caused. Skulls of the Foe makes this test even more dangerous for your opponent.
(Bad) Often limited Line of Sight. Small template - few hits. Scattered effect. Chance to miscast.
(Good) Gives enemy Wizards -1 to Cast. Light of Death makes your other Incantations to go through. If not dispelled, LoD is a very global spell that can cause much harm to Units. Coldblooded Units get no extra dice.
(Bad) Forces one of your LPs to be stationary. Easy target for enemy "Hunters" - such as Gorgers, Miners, Gutter Runners etc... Costs alot!
That was a rough summary, so don't execute me if I missed something
First thing to think of, if you want to decide on only one of these two: Which armies do I face alot where I game? How do they play? Which weaknesses have these armies? What should I be careful with? What can really hurt me? How can I counter that Unit?
When you've answered all of those questions, I'm sure you're close to your own definite answer.
Personally, I like the Casket a little bit more ( though I love them both endlessly <333 ). In a 1250 points Tourney List, I would include him. In a 1000 points Tourney List, I would not include him, sinc it's much more of a problem with points at that level. Basically, the 250 extra points I get encourages me to field a Basket.
Note: I ALWAYS upgrade my SSC with Skulls of the Foe (except from single friendly games when I KNOW that I will face Undead or Daemons).
Hope This Helps You!