Ahh, had to open the previbable can of oil worms didn't you!!
Opinions are varied and vast.
Here's all I have to say: Modern oils are modern so any rated for MC use(JASO approved), regular, synthetic or a blend, and at a viscosity recommended by the MFG and correct for your area and seasons of riding will be fine if you change it on a normal schedule or before.
Personally I'm trying Shell Rotella T6 full synthetic and plan on changing it every 3K since the changes done by me are about $25. Have only 600 miles on the new oil. So far so good but too new to give a glowing endorsement. And, yes, it is 5w-40 but I ride into the mid 40's so the lower viscosity there will be beneficial IMO. During the summer I doubt there would be any difference from 10w-40 considering the bike would be at 80-90 before even being started.
I can say that like new tires, the initial change was very noticeable from how the old worn oil was but of course that was expected.
Final thought, go with what you feel comfortable with and if it doesn't work change it out. You aren't going to blow a motor etc. as long as the oil is JASO approved. Some might be quieter or shift better for you but besides that I'd be hard pressed to see a difference in 3-4K miles of "normal" use. Just my .02