I would just measure what you now have and go for something similar - make adjustments based on what you like/dislike about your current bike(s). For example, if you have a road/racing bike and want something more relaxed for touring, you probably want less steep head tube and seat tube angles and a long chain stay. Also don't be overly concerned about too long or short tt - stem lengths compensate and don't affect handling much at all unless you go to extremes like a 70/80 or a 130/140. Do a search and there are a couple very informative threads on this subject.

Many frames are built "square" with the tt and st being about the same. I think that's what you are referring to. That's fine if that's what fits you but I go back to seeing what you now ride and are comfortable with. Also most frames built over the last 10-12 years have sloping tt's so you need to be concerned with "virtual" tt rather than actual. For example the st might measure 52cm but the "virtual" assuming you have a horizontal tt might be 56cm.