Choose whichever of them you like best.选一个你最喜欢的吧。
Whichever of them are you going to help?你究竟帮助他们当中的哪一个?

whichever也可用作疑问限定词。例如:
Whichever book do you like?你到底喜欢哪一本书?
Whichever day you come, we will be pleased to see you.无论你哪一天来,我们都很高兴。