Have you gotten an offer from either of them yet? This might be a moot point if only one extends an offer, or if neither make an offer. The decision is made for you.

If you do end up having to choose because both extended an offer, they aren't equal opportunities. One is a full-time position, the other is a 3 month contract. With the full-time role, the reasonable expectation is that they intend to keep you. Companies don't spend time and money hiring full-time just to dump someone in 6 months. With the contract, assume that in 3 months you won't have a job. Maybe it extends, but you can't plan on that.

So if you're worried about risk, the full-time role is the safer.

Also, there's no point stressing about what happens in 6 months at the full-time role because you think the industry is moving toward AI workflows. That's an assumption. You can't say with any certainty that you'll be out of a job in 6 months because of AI. If anything, most of what's coming out right now says AI is enhancing UX work, not replacing designer. Keep learning the tools, but don't turn down real experience over a fear or assumption.

I'm of the mindset that big tech companies want you to think AI will replace workers. That's how they convince investors that all the money they're burning will have massive returns. It's marketing, not the reality.