If you are planning on taking long flights with kitty onboard, even sitting next to you, then you will be choosing quite a different carrier from the style that would be used when your cat flies in the cargo hold.
Take off whenever you want, go where you will, and let your dog ride right beside you, not in a stuffy cargo hold.
Although the number of incidents have declined in recent years, dogs do still sometimes get lost in transit, escape on the tarmac, and even die in the cargo hold.