CK2 and Victoria 2 are completely different games. Victoria 2 is like a more complex Europa Universalis, but is set in the 19th and 20th centuries. The latter point was reason enough for me to buy it.
The choice depends on what you like in a strategy game. If you like the idea of playing as a country, colonizing large parts of the world, defeating your rivals in Great Wars and becoming the premier world power, then I'd go with Victoria 2.
CK2 is very fun in that you play as people in a dynasty instead of a country. It's fun and novel, but I still prefer to play as a country. So if you end up getting CK2, know that it will be a much different game.
I'd also like to point out that the complete list of DLC for CK2 raises the price tag pretty high. In the end, I suggest you buy both and decide which one you like better, then get the DLC. Victoria 2 is starting to look dated, but graphics shouldn't be a deal-breaker for you. If it was, you'd be better off playing something like Total War.
EDIT: I guess I should read the whole thread. It's good that you decided to get both.