Go with #1...That option will save you some money and be plenty of light for growing about any plant since you don't have the depth to worry about in a 20G long. I use one 65 watt PC on mine and I grow anything I want.
I would just get one 55W kit. I'm using it with the GE 9325K bulb on my 20H (4" taller than yours), and getting excellent results. Your shorter depth should make 55W more than nessecary, and If higher, you might be getting into algea risks.
Have you considered a double or triple normal flourescent? I'm using a triple tube on a 38 gallon and I really like it. Not sure if they make one for that size but it is All Glass and comes with the 30 watt 9325K bulbs in the 36 inch long strip I have.
With 2 or 3 bulbs you'll have better coverage, no dim areas near the surface.
I considered getting one 55 watt, but its only 22 inches long and the tank is 30". I'm afraid that the edges of the tank would not get bright enough light and the plants would grow angled towards the stronger light. The 13 watt kit would be 8 inches long and would fit perfectly on the end.
THe problem with standard flourescents is that the closest size to 30" is 24", not to mention that to get a triple tube strip light would probally be just as expensive.