However
In what way; regardless of how. It can also be used to introduce a
statement that contrasts with something that has been said previously.
E.g. The book is expensive; however, it’s worth it.

Whichever
Anyone from a limited set.
E.g. Choose whichever ring you like, it’s your birthday.

Whatever
Everything or anything at all, no matter what
E.g Please take whatever you want from the fridge if you feel hungry.

Whenever
At whatever time, every time that
E.g. We can leave whenever you’re ready.