Not to confuse you but I'm 5'5" with a 30 inch standover. I have several bikes. My Trek Navigator is 16.5, my full suspension Kona is 15", My hardtail Kona is 16", my Gary Fisher XC suspension is 17" and my roadie is a compact 50cm (custom so I know it's right). Please take note that the mountain bikes will have a smaller frame that allows the rider to move around with the bumps and rocks of mountain biking.

Top tube length is more important than seat tube length (what the frame is usually measured by in inches) because some may feel too cramped or too stretched. For the kind of riding hybrid user do, I would suggest a clearance of the top tube by one inch, you don't want to really touch the bar or be too far from it. Hence the reason for geometry listings on the websites. Easier that way to figure.