Venice vs. Las Vegas: Where should I take my dream trip?

My partner and I are planning a major trip and are completely torn between Venice and Las Vegas. We love beautiful scenery and history, which makes Venice incredibly appealing, but we also crave high-energy nightlife and big-city entertainment, which points us toward Vegas. We are trying to decide if we want a cultural immersion experience or a pure party atmosphere. Does anyone who has been to both think the contrast is as dramatic as I imagine? Also, if we are looking for a mix, are there any good compromises or suggestions for blending the two vibes? Any advice on which one is better for a first-time couple's getaway would be hugely appreciated.