Honda's are bomb proof. Yamaha's are nearly so. Everything else be careful what you buy used. Ninja? Crotch rockets are cool but you will get tired of commuting on one and insurance is bad especially for a newbie. Hard to put a chick on a crotch rocket and be safe too, non of them are built for comfortable two up riding. A cruiser is just as fast for a commute and you are less likely to become paralized in your first year. Get a motorcycle traing course first...I did and it saved my life. After you have 5000 miles under your belt then you will be ready to make an informed choice and if you buy right the first time you won't lose much cash in the exchange which is more than worth the education you need to be safe in traffic on a bike. Hell, a 750cc anything will scare the hell out of you at first wrt acceleration, so go slow and keep the shiny side up.

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Well I guess this ain't gonna be easy.......