Actually a 90 degree (or "L") V-twin does a good job of cancelling out its own vibration, even without counter balancers. Those "big" cylinders create gobs of torque. Point one cylinder toward the front tire, then rotate it until it is almost horizontal and you solve most of the cooling problems and get a very low center of gravity. It is an inherently excellent design. Check out anything that Ducati makes or the Suzuki SV or DL series bikes. That's why v-twins still exist.
P.S. As already noted, the Boxer engine and vertical twin are both twins, but not v-twins. Also, as noted by a certain comedian, the secret to enlightenment is fourteen year old blonde twins.
...oh so right! I've been trying to choose a new ride now for over a year. My head says inline four...hayabusa, possible sport tourer with mods...very fast not too radical etc...then I hear a Honda RC 51 go by...wow! that sound is intoxicating...more expensive, less power and less versatile...what to do? all because the I-4s seem to buzz me out too much.