You should give a definitive answer because they ask for one, yes, but not before telling them why. You should start by giving a few arguments for and against striking. Obviously this is a huge topic but some examples include
+ contracts could affect patient safety negatively in the long run
- striking could affect patient safety in the short term (although depending on who strikes - e.g. A&E shutting down vs pushing some non-urgent consultations to later in the week)
+ contracts not fair to junior doctors and they should have the right to protest just as any other profession
- striking could affect negatively the public's perception of doctors, e.g. "they're just in it for the money" or whatever
And so on, you get the point. After you've listed some pros and cons you need to briefly tell them what you choose and why. Personally I might say something like "even though striking would have some negative consequences in the short term, I think it would be a price worth paying for the long term benefits so I would probably strike".