I have not made a big deal of this. I was an environmental engineer of the EPA and I have spent a lot of time working on the problem of global warming since I retired. You can quit working, but you can't quit thinking I guess.
Each year the Government is required to make a report to the United Nations on the emissions of greenhouse gases and the people who work on it do a pretty good job of covering all the bases. But, and its a big one, they make it clear that water is the dominate greenhouse gas.
We have know that H2O was dominate in global warming for, well forever. If you have the new CRC Handbook of Chemistry and Physics they show how much and of what wave-length of sun light the different compounds take out of what is coming in and exiting our atmosphere. Carbon dioxide takes energy at lower wavelengths, and it releases the same wavelengths or some lower fraction there of based upon quantum orbit theory. Water does the same thing, but water is like mother-ship while CO2 are like the drones.
Water has been ignored because it was believed that the level of water in the atmosphere is constant. It is not. The amount present at higher levels in the atmosphere is rising and this is far mor dangerous then CO2.
To give you some relation between the amount of CO2 and H2O in the air, image that you have a cubic meter of air at 1 atmosphere at sea level and about 80 degrees F and that the relative humidity is a relativly low 50%. So in the m^3 you will have 2.55 lbs of air, (0.011 * 2.55) = 0.0281 lbs water with a volume of 0.620 ft^3 or 17.6 L of water vapor. So if the average [CO2] in 2004 was 377 ppm we will adjust it to, say 385 today. Thus 385 ppm of 1000 - 17.6 L is the volume of CO2 that you would have. That is (982.4)*0.000385 = 0.378 L CO2.
So you have 17.6 L of a much worse gas vs 0.378 L (a coke can holds 0.355 L so a cylinder the height and diameter of a coke can is greater in volume then the CO2 in the air. Which, by the way would almost double in the m^3 if I opened a can of coke.
Most of the CO2 we release is easily controlled. Every where you see a smokestack you see a source of CO2 or worse pollutants. Please pardon my english, but the purpose for smokestacks is to spread your crap on to your neighbors!
If we used technology available today, at least I hope some one smarter then me has thought of it because I can design it right now, it is possible to take the stack emissions of all stack emissions of CO2 and use them for green purposes such as growing food. There may be no profit in the food, other then avoiding the fines for discharging, but the number of jobs and opportunities for growth is enormous.
The answer to your question is that you want a fast growing plant that can be used for other purposes, such as by farmers. Slow growing plants do not store or sequestor, very much CO2 because what they absorb in the day they release at night. Broad leaf trees may appear good but if they loss their leaves then you have a situation where about 1/2 of the carbon, as in composting goes of as CO2.
Also remember that fossil fuels and all of the alternative that we have are either hydrocarbons or come from hydrocarbons as in the case of electricity. Even when you burn ethanol, Pres. Bush's new baby,(no one has realized that everything he talked about in that speech was in the Popular Science Magazine that was on the newsrack at that time. Maybe it was Popular Mechanics, I don't see him as a science kind of guy.) You get two CO2s but six H2Os.
I hope I have helped.