πάντως means "in any case"
Example: Πάντως εγώ θα έρθω. = I will come in any case.
Sometimes "πάντως" indicates a contradiction when the speaker wants to differentiate himself from something.
Example: Δεν ξέρω τι θα κάνεις εσύ, εγώ πάντως θα έρθω. = I don't know what you will do, but I will come in any case.
"ωστόσο" means "however"
Ήμουν άρωστος. Ωστόσο πήγα στη δουλειά. = I was ill. However I went to work.