If you are developing a Plugin, most places I have read recomend to go OOP, if you are developing a theme or for a theme, the recomendation is to go with pluiggable functions. This is functios wrapped in an if that determines if the function has already been defined, anybody can later on override you function, normally in the functions.php script.

Now for plugins there are some skeletons or boilerplate that using oop separate admin functions from public functions, and also separate logic from presentation. And also put hooks all in the same place. You can search a bit on this a find one you feel confortable with.

In the body of your question, you are talking about two different things... html is a client side language where as OOP stands for Object-Oriented Programming --- which is a programming paradigm and has it\'s applications in languages such as Java, Python, Ruby, etc.

PHP on the other hand, allows one to program either procedurally or OOP

So the question is not which to pick... it\'s whatever style you are comfortable with (I recommend going the OOP route).

Lastly, which ever you pick, you will be writing HTML for things like radio buttons, input boxes, etc. on the settings view. And speaking of views, if you go the MVC route (which stands for Model-View-Controller---which is an architectural pattern---your HTML will be inside the View

It will be best , if you will go to build WP plugin through OOPS . Because you don’t really have to worry about clashing with functions defined elsewhere .