the Inline 6 offers far better balance than a V6 engine, this is because of the odd number of cylinders per bank, often a balancing shaft is required to assist the V6's engine balance, in an inline 6, most types share similar crank layouts (7 main bearing) simple because it offers excellent balance, and allows for a larger bore and stroke with in a reletivly compact block, while the V6 is smaller it is limited in size simply because of the balance characteristics, an inline 6 all produces better torque charactiristics as well allowing for better lower end torque compared to a V6. balance is the same reason that their is no inline 8's a V8 with it's block set a 90 degrees, which is common to most Ford, GMH and Chrysler V8's offers the best balance of any engine type, even better than the horizontally opposed 6 used by porsche. the V8 allows for a compact but high capacity engine, with a straight eight the crank shaft is far to long and torsional vibration becomes a massive problem, it requires a large and heavy harmonic balancer to correct it. smaller lighter balancer's can be used on the inline 6 and V8 and this allows for a very smooth operation, good torque charactristics, generally good reverbility.