Respect your client’s preferences and personal tastes. They will inherit and live with the code you leave behind. If they don’t feel comfortable with some part (even if it works perfectly) they have a legitimate reason to change it to something more manageable.
You are not owner of that code. You are writing it for him/her to own.
Imagine you are a carpenter making a dressing table for a client. Is your personal taste or client’s taste more important?
In fast-paced finance IT, sometimes you can be forgiven to adopt your personal favorite choice (rather than client’s favorite) to help you get things done fast — since you are the coder. I feel in some contexts time-to-market is still the paramount consideration.