I own both bikes and the Busa is a much more enjoyable machine. The build quality and fit and finish seem better on the R1. The R1 is fun to scream around on and I believe it is easier to race with because the power and torque are not as explosive as the Busa.
The R1 has to be wound up to around 7,000 RPM's before it starts making great power. With that said, the R1 is easier for me to launch because I don't have to worry about sending the tire up in smoke. When you go full throttle in 1st the front end will begin to lift as the RPM's climb over 7,000 and it will continue to lift up until 15,000 rpms. Then if you hit second really hard it will snap right back up until around 130-140 and then slowly set back down.
Now keep in mind this is not an intentional wheelie, the bike just wants to lift. You can keep the front down in second but only if you let off for a split second.
Now lets talk about comfort. The undertail exhaust looks really cool, but it is hot as hell in the summer time and very uncomfortable. The R1 slams over the smallest ripple in the pavement and jars your head around. You can ride the bike all day long and not get sore as long as you are racing around. If you try to just pace the ride and cruise you will be crying for mercy after 75 miles.
The Busa is a faster straight line bike but takes a little more skill to launch well. It pulls double duty as a comfortable cruiser and all out performer. The Busa also lends itself well to a novice rider. I say this because the seating position feels like you are sitting in the bike like a cruiser, where the R1 makes you feel like you are perched on top of it. This makes leaning into corners feel much more relaxed and confidence inspiring. Just don't nail the throttle in 1st with cold tires because they will be howling in protest and coughing up smoke.
To sum things up for you, I have not ridden my R1 since I got my Busa. That should pretty much tell you everything you need to know.