For starters, let's look at costs. Gondola working hours are generally from 9am onwards and can go on up to 3am. Until 7pm, rides are priced at a standard €80. Post 7pm, the ride costs €100, with an extra €40 for every additional 20 minutes. So, whether or not you should take a morning or evening ride depends on your budget and convenience.
Next, consider whether you want a shared or private experience. In a shared experience, while you won't get a say in who your co-passengers will be, you can still enjoy the gondola experience. In a private experience, you can book out the whole gondola for you and your loved ones, albeit at a higher cost.
You can also decide your ride based on whether you want live entertainment or not. If you're seeking a serenade experience, you'll have to book that separately.