First, let's deal with the far east imports. Japanese bikes tent to run very well for a few years. Then they fall apart, you toss them in the nearest rubbish bin and never miss them because they have slightly less personality than a clothes dryer. Many have serious stability problems which highly practiced riders can turn to their advantage. Styling ranges from the bazaar to blatant Harly copies.
Harley: Mechanically sound design. These bikes have long had a reputation for being infinitely rebuildable because of the design and parts availability. There are many over 60 years old that are daily riders. All the electric bits are imported from Japan. Naturally they won't be sending their best parts to their main competition so, not surprisingly, most Harley problems are electrical. Handling varies from one model to the next and ranges from decent to majestic. Harleys tend to be expensive and parts for them are usually expensive. One advantage is that the frame geometry is such that you can make some rather radical modifications without hurting the handling. One very big disadvantage is that you will need a tracking device at most motorcycle functions to figure out which one is yours.
Triumph: Impressive engineering, these bikes are designed to last. They have made a special effort to minimize the number of far eastern parts, buying locally as much as possible. Handling is very good and very well behaved. This is the only bike of its size that is good natured enough for a first timer. At a motorcycle related event, you can spot your bike from several blocks away by looking for the crowd of admirers. While not likely to set any world records without some modifications, the Bonneville derivatives are able to keep up very well in a group ride and can reach the speed limit on any public road in the US without straining. In fact, there are many larger bikes that can't catch the Triumph twins. And yes, they have personality. Triumphs are much like an old friend that you can rely on.