Which one do we natives say? Well, it's not so straightforward! I get asked this question surprisingly often so let me shed light on how we actually use these prepositions as well as alternatives 😎
AT + place = very general. It doesn't give an exact location (inside, outside. on the roof, round the back etc). If you are somewhere large, AT might be confusing. If the location is somewhere small, like a bus stop, AT is fine. Example:
- Paul, where are you?
- At the cinema. (General location without being specific)
- I'll be there to meet you in 5 minutes. So where can I find you?
- At the cinema!
- Where exactly?
- At the cinema!
- Nu, blin, inside, outside, in the toilets, by the ticket booth? Where?
- Ah, inside near the popcorn stand!
- Paul, you annoy me! I'll be waiting at (by) the main entrance after you've finished watching the film!
IN + place = Inside. Very simple (But i'll give you more natural alternatives)
- Let's go to the cinema tonight.
- Ok, I'll be getting there early so I'll meet you in the cinema! (Better: I'll meet you inside)
- I'll be at Waterloo Station around 5pm (General location. Still won't be able to find you)
- Ok. I'll be in the station near the platform waiting for you.
So to sound more natural, unless the location is small like a bus stop, entrance, door etc (AT), we prefer to be more specific: inside, outside, by, near etc. if the location is large.