Nashua is smaller, more sparse. Still has a city feel in some areas, but it doesn’t bustle with the quite the same life as Manchester does. Manch has a lot of college-aged/young adult folk who enjoy going out. Downtown can be pretty lively. Tons of restaurants/bars. You’ve got the arena there, too, where many events (concerts, graduations) are held. The city’s board does a good job keeping city events happening as well (food-themed events/local business promotion/etc.) If you are between these two and looking for fun, I’d say Manchester. You’d be close to work, and within two hours either direction you could be in Boston for a night out or on a hike in the mountains.