Having owned V-twins (both sport bike and cruisers/tourers) and in-line 4-cylinders, I prefer the visceral sensation of the V-twin. The 4-cylinders tend to be more like sewing machines. Very reliable and better from an engineering perspective, but the V-twins are also a nice layout for a motorcycle. I've owned a couple V-4 (Honda Interceptor and Yamaha V-Max) and those were fun engines, although the V-Max had the worst suspension and brakes of any bike I've ever ridden. Scratch that, second worst - the worst was the Yamaha Stratoliner.
If you're going to go V-Twin and not a sportbike, get a Harley. I've owned and ridden Japanese V-twins (owned a VTX 1800, RC51, TL1000, ridden a VStar 650 and a few others). The Japanese V-twin sportbikes are awesome. But the cruisers are lackluster. They just don't feel "right." The Harley has a real V-twin feel and sound, and in my opinion they're much nicer to ride. My VTX 1800 was stupidly top heavy which made low speed handling annoying. This seems common on big Jap bikes. The Harleys have a much lower CG, which is much nicer in my opinion.
Steingar is correct that they don't handle great, so that's worthy of consideration. But unlike the sport bikes that I wasn't happy going under 90 on, the Harleys I'm just as happy going 45 as I am going 85. We've got a Street Glide and an Ultra Classic (wife's is the Street Glide). Both great bikes, love them. Every now and then I think about another sportbike, but really I like the bikes we have. The Ultra Classic is great for riding to work. Room for my backpack and lunch box in the tour pack, room for most normal errands I may run (including small grocery runs), comfy, cruise control, etc. Besides, it's flat here, not like I'm going to have twisties to enjoy.
Now if you want a 4-cylinder bike, there are plenty of great Japanese options, and that's another story for which I have different opinions.