Personally, I prefer doing it in code. With the Autolayout Constraints syntax in iOS 9+, it relatively easy and understandable.
1. The storyboard/interface builder is excellent for creating quick and straightforward screens for a quick demo, but when the project gets larger with multiple people working on the project, then you run into problems with version control conflicts and constraints get quite messy on more complicated views.
2. The screen size on laptops is too small for storyboards. On larger projects, even with a 27" iMac, it becomes unwieldy.
3. Your hands spend more time on the keyboard, and you can jump around a project quickly using Cmd+Shift+O. Searching in a large storyboard is not easy.
4. As it is all text, refactoring is a lot easier (when Xcode gets proper refactoring for Swift). Also, conflicts are easier to manage.
5. Cell identifiers and storyboard ID strings are the cause for a lot of crashes and can be difficult to debug.
6. Refactoring IBOutlet's and IBAction's can cause problems and crashes if the links are broken. The selector in Swift has been improved, so it will not compile if the method is invalid.
If you are going to take the code approach then I highly recommend using MVC from the very start, otherwise the controller gets massive, or consider an MVVM approach.