My Dm said that we are going to restart soon and I'm going to be a druid. For a druid, the key to success is an animal companion. I've been a druid before with an animal companion, both of us never died so it's good to have one. I'm thinking of having a Spinosaurus because not only does it have a swim speed and can hold it's breath but it has the ability swallow whole. When it's large it can swallow a medium sized person. Is this a good choice? I need suggestions. Thanks.
While the animal companion is a great part of the druid, I wouldnt consider it the most important part. It isn't like the summoner and the eidolon. I'd say the key to success is making sure you know what you want to do with your druid itself. If you want to focus on casting with your druid and use wildshape for utility, then I'd agree with treantmonk and say you might want to take the domain instead. If you want to focus on fighting in wildshaped form then the Animal Companion is a better choice.
The key is to decide what you want to do with the druid and focus on that, because if you try to do it all, you will likely end up rather flat.
Kolokotroni I understand what you're saying but I'd prefer an animal companion with a druid.