So where is the Tristan? I limited each tier to only six ships - which means there are plenty of good ships, like the Tristan, that did not make the cut. In the current meta the Tristan has lost some of its historic luster. Sadly, but it is the truth. It is increasingly difficult for any T1 Frigate to not only find solo content, but survive it once it has been found. That is just the reality of Eve today.
So what I tried to do was create five tiers and rank the six best ships at each of those parameters. All-Around ships, like the Comet, perform under a very, very wide window of engagement. As do the other ships on the list. Those engagement windows are different for each one of these ships, but they are all very wide. And the Hecate makes it because it also can probe.
Situational Best are ships that I feel are the best at more specific goals than the all-around ships. The windows are smaller, but still impressive. But in these ships you really run the risk of picking the wrong engagement and getting your ass handed to you. But these remain strong performers when it comes to solo.
Reliable Best are the workhorses of solo. And it is no surprise that most of them are range kiters with the exception of the Legion (although not always). These ships are good at what they do, but what they do is just more situational than those above them.
Tight Windows are obvious, at least to me. You can't slide a Vargur into a novice plex and its engagement window is very small, unless it isn't. These ships are great at one task and for each of them that task is different. But they are not great generalists.
Wingman Needed. These ships can be awesome, but they can struggle at solo in many situations. So you might want a friend along to be bait, hold point, or help you find targets. This doesn't mean they can kill ships on their own, but they could struggle to do so.
Anyway, I'm already debating some of my choices here and I'm sure you have your own thoughts.