There's a saying that attempts to describe the age old discussion around horsepower and torque: "Horsepower is how fast you hit the wall, torque is how far you move it."
While that creates an interesting visual it only kind of explains things. Here's a bit more of a specific explanation. Torque is force acting on something from a distance. Think of a ratchet when you need to break loose a stuck bolt. If you slip a longer pipe over the end of the ratchet it generates more torque, breaking the stuck nut loose. Or in an engine's case, a piston pushing on a crankshaft using leverage to move it.
Horsepower is a measurement of power, the rate at which work is done or torque multiplied by RPM. Think of it like this. If you run out of gas on your bike and have to push it two blocks to the gas station it may take you 5 minutes, if someone helps you push it, it may only take 3 minutes. The same of mount of work is being done in less time due to more horsepower (or in this case manpower).
At their base explanations those are the definitions of horsepower and torque, but we know in the garage leaning up against the bench on a Saturday afternoon the discussion doesn't stop there. There will forever be arguments over what is better, horsepower or torque, and I could get off into the weeds about how to manipulate both, but I don't think its about that, it's about riding style.
Which is why the argument will never be won by either side. How you choose to use your motorcycle determines your riding style and in turn will develop your opinion on the horsepower vs torque argument. And when I reference how you choose to use your motorcycle I don't mean street use vs dirt or touring vs road racing, I am referring to how you specifically operate your machine in different types of situations. A good example is the four-stroke vs two-stroke argument. Both could be used for woods riding but some folks will be more comfortable on a 300cc two-stroke and others will feel better with a 450 four-stroke. There isn't a wrong answer, just a personal preference.
Historically the cruiser folks have long touted the torque numbers on their motorcycles, with OEMs like The Motor Company not even bothering to list horsepower numbers. Take the current 107" Milwaukee-Eight engine, the listed torque number from H-D is 111 lb-ft., which sounds like an impressive number and is a good number. What they don't list is the horsepower number which on most dynos around the country is a paltry 75-77 horsepower. Are the horsepower specs left off the sheet because they are embarrassing or because the demographic doesn't care? By design the classic V-Twin engine makes good torque, the long stroke, smallish bore engines operate much like the original example of a wrench with a pipe on it. The longer stroke doesn't require much force to generate the larger torque number and while they typically don't play well at higher RPM, they generally don't put out horsepower at the same efficiency as an overbore motor that spins up quicker and farther into the RPM range. But it seems to favor the touring-style rider with a heavier bike that packs it full of luggage and motors across the country. But, I'm not exactly sold on the idea that torque is king.
Ultimately you can manipulate torque with gearing, whereas if you are lacking in horsepower, you can't make up for that. Or you can simply adjust your riding style to accommodate for the situation. I tend to lean toward a bike not just with big horsepower numbers but the better power-to-weight ratios. My Husqvarna Svartpilen 701 is a good example. Weighing 347 wet and making 70 hp, it has a good power-to-weight ratio and its peak torque is only 48 lb-ft. way up in the 6,800 rpm range. I don't ride that bike under 4,000 rpm. I love to keep that little Single humming and keep the wood laid to 'er and it keeps a smile on my face. I've said all that to say this - ride what makes you happy and keep 'er pinned.