29er are very late 2000's; 27.5/650b is where it is now....

For the specs, jut pick the color of the bike you like more at this price point, as there is too little inbetween them; as a very basic rule, 29er vs 27.5 if your over 6" would go for 29er, under 27.5. but if your starting out, you don't have anything to compare it with, so just go with which you like best.