Penzoil is pretty popular.

I started using walmart oil in my outboards first in a new 1982 suzuki DT-60 and never had an engine problem; next was a new 1999 suzuki DT-140 and it is still running with never an oil related problem. Just bought a 1993 mercury 90 HP and it had been using walmart oil and still runs great and has 120 PSI compression in all three cylinders. Now that 140 suzuki, Ive done much offshore with it going 60 to 100 miles a day and there's no telling how many gallons of walmart oil it's used. Good luck

Ok, here's a different side.
In '99 heard all the banter back and forth, it's just as good, it's not. blah blah blah.
I got a new motor every year, always ran merc oil. Usual use was right at 500 hours a year. Some years a little more, some a little less, but pretty close every year. Every year when it was time to turn them, would do a complete inspection, compression/leak down, bearings, the whole motor. Every year always was A++.

So, THAT year on a 225 EFI, ran nothing but wally oil. Ran it just like every other year, nothing more, nothing less.
At the end of year inspection, that motor was worn out. 92 compression on all six, slop in bearings, huge amount of carbon build up. That wasn't scientific, but it was good enough for me, I wouldn't run that junk in my weedeater.
Out of all the things you can scrimp on, why in the world would it be the most important thing you put in your motor?

Stick with Yamalube. OEM house brands have been treated with additives specific for your brand of motor. Yamaha doesn't make the oil, but they make the recipe of the additives blended to it. There is a reason it cost more.