you need to chill out and realize the cycling industry is 99% fueled by buzz words and marketing. Yeah, there has been technological advancements but a bike from 30, hell, 40 years ago is still very viable, especially if the old frame is updated with modern components.
Lurk /bqg/, read sheldon brown, and learn shit than be spoon fed info everyone will disagree about here except 90's rigid mtb with slicks.>Well, you obviously don't build a bike from parts
You definitely can but it's for a completely different reason than why /g/ builds a rig. Building a bike actually cost a lot more money than buying one prebuilt due to parts market up charge but a custom build allows you to select specific parts if you know your measurements for a well fitted bike.
DO NOT SKIP BIKE SIZING AND FIT
Not only is a properly fitted bike much more comfortable but it's important to prevent possible injuries, some of which can be permanent chronic pain.
Finally, this is the last of the spoon fed info I'm giving, know what type of cycling you want to do, (mtb/road/urban/whatever) what type of terrain you plan to ride, and your budget and post that in the /bbg/. The reason there's a lot of different disciplines/classes of bikes is because cycling tech always compromises one aspect for an increase in another. There is no best bike that is good in all conditions... except 90's rigid mtb