I use Bel Ray EXS Synthetic Superbike oil. There are quite a few good oil manufacturers out there, and you normally get what you pay for. Motul makes a good oil, but it can be hard to find and sometimes costly. Whatever you do, make sure you use a quality motorcycle oil. There is a huge difference between car and bike oil. Car oils lubricate the inside of the engine the same as bike oils do, and cost less than half as much, which tempts a lot of bike owners. What you must realize is that bike oil also must lubricate the transmission and the clutch in your bike. If you use car oil, usually the first thing to happen will be a slipping/destroyed clutch. If you are easy on the clutch though, you will just wear your engine out. Oils have additives in them to do various jobs, the most important in bikes are the anti-shear additives. Picture an oil molecule as a piece of plastic. Not bad lubricating qualities, and the thickness or viscosity of the oil would relate to the size of the piece of plastic. In the engine the oil takes up the space between the moving parts so they don't touch each other, they ride on the film of oil. But the gears in the transmission will cut or shear the oil as it gets caught between them. If the pieces of plastic are cut in half enough times, pretty soon they are so thin they cannot take up the space between the engine parts and metal to metal contact occurs, causing wear.
Also, for much the same reason, most synthetic motorcycle oils use an esther base, which I believe is an organic oil base (like vegetable oil) wheras most car synthetics are petroleum based. The esther base is much more costly to produce and has a lower demand so the prices are higher.
Synthetics are not the only way to go, but the synthetic base oil will accept more/better additives, and will maintain its viscosity over a wider temperature range. That is important to me as I live in a climate where the temperature will range from 40F when I start riding in the spring to 110+F in the middle of summer.