Shyvana or Sejuani

If u dont have tank in team then its better Saj, if i knew to play Shiv, would take her only if we had tank on top and tanky support with rly good CC. Problem with shiv is that she needs to get fed, otherwise she will die in sec, and be useless, Saj will get tanky eventually and she bring so much CC

 

Shyvana needs to get close to enemy adc and to attack him. If enemy adc kites her and if she gets CC-ed she won't do that much. Sejuani just can stun 5 men and what you want more.. Sejuani is really great and better if your team can follow you, if you are in low elo Shyvana is better because enemy adc there won't kite that well, enemy team won't protect ..
Shyvana for low elo.
Seju for high.
That is my opinion, ofc you can play Shyvana in high elo as well if you are good Shyvana. You can find good Shyvana in high elo but if you are beginer first train her on normals.