It's really up to you what you like. My gf have the i-stick 30w with an aspire nautilus. Also with a 1.8 ohm coil. She vapes it at 14 watts, and that's where she likes it. But if I were to use it I would probably turn it up to around 19 watts. So it's realy a matter of taste. As for the lifetime on your coils. The higher the wattage, the shorter the lifespan. But wouldn't you rather have a good vape, and change out your coil a bit more often?