User have to choose type of food (from 3 or 4 choices) in our application. Default selection is used in 60 - 70% of cases. What will be better: dropdown or radio buttons?
It's impossible to give any meaningful rules on UI that would hold across all contexts. You might want to refer to your platform's UX guidelines for some guidance.
For the situation you describe, both widgets are probably reasonable choices. Radio buttons are useful if you want to emphasize the other available choices (e.g. to clarify the level of abstraction or precision), especially if the default choice is not very informative (e.g. “standard menu”). A drop-down list might be somewhat easier to operate with a keyboard, if a lot of data-entry is expected and users know the choices beforehand. It can also be adapted to allow users to enter something else (“combobox”). A big factor will be screen real estate, you can often save some space with a drop-down listbox compared to radio buttons.
If you really want to get to the bottom of this, you would have to test it with your own users but in most cases, it probably doesn't matter that much.
According to this great article by UX Movement, using a select menu when there are only 3-4 choices available is not recommended:
When you have less than 5 options for users to select from, you should use radio buttons. This allows users to make their choice faster and easier because all they have to do is look at their options and click once. With a select menu, users have to click the menu, scroll to an option and click again. A select menu also keeps the other options hidden until the user clicks it. When you have less than 5 options, it’s better to visibly lay them all out on the form with radio buttons so that users can scan them quicker.
You can find much more about how to (not) use the select menu here in the aforementioned article: http://uxmovement.com/forms/stop-misusing-select-menus/
Radio buttons are better if the number of options is absolutely limited. I am currently designing a solution including a set of radio buttons plus an option for "Other". The list of fixed options will always be the same, but there are possibilities for extra choices. This is based on what the clients would like.
If you have the screen space, using radio buttons for the sort of solution you are describing would seem to be the appropriate solution.
If you have more than three options you can got for dropdown eg: yes/no - Radio button True/False - Radio button male/Female - Radio button
If we know that there is no increasing in options we can go for Radio button where user can select in single click and visibility is clear.
If we have lot of options and need to be dynamic we can prefer for dropdown.
Every case is a special case when it comes to UI design, so you should always experiment and see how well actual users understand your designs. But the image below should help you get to a first approximation of what might be a good choice.
(And also read this article by Jakob Nielsen.)
If the number of answer options is less than two, then we should avoid using dropdown button. This is because the survey participant has to click on the button to see the answer options and he/she might get annoyed if there are only two answer options. Instead, it's better to use a radio button if there are 3 or 4 answer options.