Is a 2 piece crank better than a 3 piece (bikes)?

Question

Is a 2 piece crank better than a 3 piece (bikes)?

Answer 1

The 2-pc cranks developed as a complement to newer bottom brackets that were aiming to be more durable by spacing the bearings farther apart than what was possible with cartridge bottom brackets and standard frame bb shells.  

So far, the newer bottom brackets (called "external bearing") seem to last longer, so it appears to be a good thing.   It all depends on the kind of riding you do, though.  Some cartridge bottom brackets are better than others, and casual riders don't usually wear them out too quickly.   If that's the case, then there really isn't any appreciable difference between a 2-pc and a 3-pc style.  

There is a smidgen of weight savings when you go with a 2-pc crank, but it's not enough to matter really.  

One thing that I like about the newer external bottom brackets/2-pc crank systems is that there is less waste when you need to replace the bottom bracket.  A couple of bearings is usually all that's needed unless there is some damage to other parts.....with the older 3-pc system, you have to replace the whole bottom bracket with spindle and shell, etc., because they aren't serviceable.  That makes more environmental sense to me.  

Besides those points, there really isn't anything better or more valuable in the crank arms and chainrings in a 2-pc over a 3-pc.