Some of the other answers here missed your true question of _what_ should be evaluated. I guide my clients around this exact problem. Even though the focus of my business is native apps, I have no problem saying "you don't need an app for that". With more details I could help you further, but in general you're asking:
Who (is using the app) - millennials and retirees use devices differently
Where (is it being used) - is it mostly going to be used on mobile? is it an extension of something else
What (kind of experience) - Web/Desktop/Mobile all have different UI conventions and limitations

That's really just the beginning! As you understand the idea better and the targets, it should become more obvious which is the better choice. If you want to call me, I can provide more detailed suggestions about an appropriate route to take with more information.