Either is correct, they just have a little different focus. The first one emphasizes that Venice is still the most beautiful city to you. The second sentence brings our attention a little bit more to the fact that your trip to Venice happened in your past.

Both are correct, as has been mentioned, but I’d like to point out another translation that works since you’re mentioning a place within a geographical location: The most beautiful place I’d ever been to was Venice, Italy. I used the comma between the names Venice and Italy because you can do list to identify a smaller place within another location. For example, to say something like: “I moved to Houston, Texas.” Also, I opted for “I’d” instead of “I’ve” to imply that you have been there but are there no longer. You could also not do this small change and it can have the same implied meaning.

Both are alright, pretty much the same meaning