Q. I want to buy bike which is best R15 V3 , Gixxer SF 250, Classic 350 or Duke 200.

R15 V3- Racing bike with committed posture, good for high speed.Gixxer SF 250- looks like racing but its in between cruising and racing bike. bike is good.( proper city bike)CLassic 350- not so good performer but its a cruiser. not a city bike( heavy traffic) DUke 200- you can race, you can easily maneuver in city. on highway its bit downside if you don't consider its hard seating its equivalent to CL350.

Depends on your riding style and for what purpose you are buying the bike