well comparing the two is a little difficult. VC just got a new Army book...Tomb Kings are a little older and are going to get upgraded...
so you gotta ask yourself...are you only wanting to win at any
cost? If so, VC is probably going to be the best option for you, since they are newer and got a better rule set right now
If you are a player, just to play...then get the army that you like best. Look at the models and what not. If the Egyptian look is your thing, Tomb Kings are were it's at.
Just think about this...you are going to be painting 100 to 150 models. You better be painting something you like!