If you're about 8 feet tall, then go full custom.
If you're about 4 feet tall, with short arms and legs, then go full custom.

But, if you're somewhere in the middle, there is a fair amount of adjustment to the bikes. Long/short stems, rise, drop, seat forward, back, up, down, long cranks, short cranks, etc.

Personally I like taking a stock frame and building it to my whims. And, I ride several bikes, and each is a little different. And, that is just fine with me.