Is Arvak Better Than Shadowmere?

Is Arvak Better Than Shadowmere? So, just wondering which horse others think is better. Shadowmere or Arvak. I personally like Arvak more, since you can summon him wherever you want, but Shadowmere is stronger in battle. Does Shadowmere disappeared after Arvak? If you interact with other horse while using Shadowmere he is “deactivated” and goes