I always love this debate... just like the spark plug debate, and the 2-stroke oil debate, and the reed debate... I'll throw my opinion out there, just for fun. I'm on board with Rich, but it's always been my approach. I go with the few extra bucks (literally, a few extra bucks) for the Merc Premium Plus High Performance. Test proven, and recommended by Merc (who knows best? Merc does) for all applications. For good reason. Lubrication, water emulsion, and so on. Here's where I get real stupid... I change it in the fall, and in the spring. It's good for the seals. I also fill it till it comes out the top, then put in the top screw, pump it a few more times to "pack" the gears (like a bearing) and then put the drain plug back in. Not too much pressure to blow seals, but enough to push it in. Feel free to tear that theory apart... It's just what I do.