It’s a tough question to answer as it’s highly subjective. People have different preferences, budgets, techniques, and applications. For this reason, the best sonar is the one that best fits your needs. I don’t believe one is better than the other, they’re simply different, with different pros and cons. The best sonar is the sonar you can afford. Flasher or fishfinder, if it helps you find fish under the ice, it’s the best. If you’re looking for the ultimate on ice, the link above to the Marcum LX-9 is very hard to beat, however. Just know you’ll need more than a thousand bucks to invest.