The 2X10 watt CFL's are certainly brighter both because they total 5 more watts and they are basically a T5 type bulb. (BTW, my tank has a glass canopy as well.) I can't grow most carpet grasses in this tank but the Helanthium tenellum (right foreground) does well with that amount of light. If you go with the T8 I would recommend adding the LED strip if it is in the 6500K spectrum you need for plant growth.
2 bulbs would put me at 34w isn't that too much for a non CO2 tank? 1 bulb at 17w would be perfect I think. Those fixtures are so pricey tho lol. Right now I'm looking at spending $45 on a T8 fixture and a bulb those fixtures alone are like $90 aren't they?