Getting the Best Fit for Your Bike
Getting the right fit for a bicycle is a lot more important than whether it's made of aluminium or carbon fibre or anything else.
You need to start by measuring your inseam.
The easiest way I have found is to use either a book or a piece of wood or short tube, push it hard up into your crotch and measure from the floor up to the top of the book / wood / tube. (Best done with some else's help)
You also need to be in bare feet - and feet only a little bit apart.Frame Size
Your inseam length will then allow you to calculate the right bicycle frame size.
It's about 67-68% of of your inseam length.Seat Height
Your inseam measurement will also allow you to calculate the correct seat height.
It should be about 88% of the inseam length from the lower point of your saddle to the pedal when it is at its lowest point. This allows for your leg to be just slightly bent when it's at full extension.Handlebars
For me, this is all about comfort. Most people find that the handlebar width should be about the same as your shoulders.
Once you're really serious about getting the best bike fit, you can get into real technical details about different tube length ratios and crank lengths - but if you get the basic stuff right, it should just come down to how comfortable it is.