Pick a company that you know a bit about and can talk about enthusiastically - probably best to go for a big company as you can find more media articles about them.
Ask yourself what challenges the company is facing then think a bit about how PwC could serve them. Have a good read through of all the services that PwC offer. Make sure you include a few of these in your answer.
If you are applying for actuarial make sure you pick a company that PwC may require actuarial consultancy services - e.g an insurance company. Focus a bit more on this section so they can see you understand the service line you have applied for.
Make sure you say why you picked the company - be enthusiastic.