Hi and welcome. I prefer the wattage mode and I think it makes a more consistent vape if you change tanks or there is a small difference in the value when you replace a coil. There's just less fiddling with it. But in truth, it doesn't really matter as either will work. As to the setting, it's a personal preference thing. I'd recommend you start in the 7-8 watt range and move it up slowly, vaping a few puffs each time, until you get something that tastes good and has good vapor production for you. Most people are going to find they like a coil of that value in the 8-15 watt range, but that's most people, no necessarily you. If it starts to taste burnt, you know you have exceeded the power level your juice or equipment likes, and you should back off a step or two. Good luck and happy vaping and welcome to the board.