It depends on your needs.
The location field from a user profile is self-declared and may have little to nothing to do with reality or actual places.
The geolocation information attached to the tweet, when present, was done so programmatically and likely is more accurate than a self-declared location. As long as you’re not storing this geodata separately from the tweet content and your use of the data will not surprise a user or violate their privacy, this information is ripe for usage as wel. You may also want to watch for the place_id attribute on tweets, which allows for a specific place instead of just lat/long coordinates.
Self-authored info about places (“I’m at the zoo”) within public tweets is pretty fair game for you to analyze as you see fit.