Steep STA and slack HTA typically indicate a frame around or under 52cm. For everyone weighing in, typically ridden frame size is a must, otherwise we might as well be trying to build a house in outer space.

I personally ride a 63.5cm (25") frame with a range of 63-65cm.

Many vintage Trek models are pretty good at keeping identical (or very similar) HTA and STA as the frame size gets larger. The bikes are proportionally larger, or at least have proportionally larger wheelbases.

It seems on small frames, the thing to avoid was toe overlap while maintaining a desired trail number. On large frames, some companies (Ciocc, Masi, etc), made the HTA steep to keep the wheelbase closer to that of say a 57cm frame--to have the 57cm frame be a sort of "sun" that the other frame sizes would work to be close to in some regard.

For high/medium/low trail, I'd categorize it as this:

High trail: mid-60s mm and up
Medium/sweet spot: 56-61mm or so
Low trail: mid-50s mm and below, with very low trail once you get into the 30s.

STA never bothers me much because I can usually achieve my needed setback amount. HTA and resulting trail amount make their characteristics known soon enough. I have bikes in all three trail length categories, and all feel good for different reasons.

*** What no one talks about, but that which I think is critical as it takes into account both fore/aft rider weight on a bike AND steering feel is: ***

Where is the front-most point of your hand/palm in relationship to the front axle??? The 'pocket' or webbing between one's thumb and index finger is by and large the forward most point of the hand (fingers not on brake levers) when riding on the hoods. From that forward-most point, draw a vertical line to the ground. Where is that line in a fore/aft relationship to the front axle?

As the distance behind the front axle increases, the rider's weight it presumably further back, making the front end light no matter what. As the "hand plane" goes further forward of the front axle, a taming effect on the steering is had (more rider weigh, more lateral effort to turn the front wheel). It's almost like you "guide" the front wheel. So a more "alert" front end is calmed, yet the bike can still maneuver quickly.

My ideal "hand plane" to front axle setback is usually around 1cm. I like a medium to lighter steering feel, and definitely notice a "slower" steering attitude when my "hand plane" is forward of the front axle.

I won't delve into hand/hood height that is much higher than the top tube (a la Technomic stem) vs. a low height. I do have ideas on that, but will echo what [MENTION=20548]JohnDThompson[/MENTION] said and that is the frame is a system and no one change happens without influencing the other.