Whats the best oil
Well, thats highly subjective to biased unfounded opinions with no scientific basis. But, based on independent lab tests, most high end/major brands synth oils are pretty good. AMSoil is very good and ive had great experiences with it and how the Honda motor/trans runs/shifts. Mobil1 gets mixed reviews, some use Royal Purple which in testing doesnt always fair that well. Some people use Shell Rotella T6 "with no issues" but there are no tests being done other than how their ass feels in the seat and how other peoples opinions sway theirs.
AMSoil, K&N, Wix (could include Napa brands if its made by Wix), Hastings filters are good. Stay away from Fram anything, they are absolutely horrid with plenty of proof.

However, the owners manual says to use 10W-30 or 40.

Can i use 20W-50?
Why? You have a water cooled motor, why the fuck would you need to clog up the bikes arteries with oil meant for air cooled motors?

Good video to watch about oil and some myths...