The perfect bike dosen't exist, but you can find a bike that approach to the perfect bike, That's the idea.-
Three principals things you want have in your bike: Stability, durability and low weight.-
Stability: You don't want fall down, you want a bike that give you the control to maneuver in all types of soils. (For example: That's one of the mains reasons why were developed full suspension bikes).-
Durability: You want a bike that resist the hits without dents and splits. (For example: That's the reason why alloys are more used than pure materials).-
Low weight
For example: that's one of the reasons why aluminium is more used than steel).-
The perfect bike would be that with 100% stability, 100% durability and 100% light. But this is impossible, then you need find the best combination of the three.-
Now, for me (ˇFor me!) in the full suspension mountain bike, the bikes approached to the perfect bike are the Specialized, because give you very good stability (4-bars linkage), and a good top tube length, not so long, not so short (they offer differents larges). They are working with M4 an alloy of sillicon, copper, magnesium, and vanadium (i'm looking for more information). All in a good not too heavy package.-