We bought a bunch of Hybrid Poplar from Musser Forest. They sell them for about $2.60 for a bareroot 2' to 3' tree and they are located back east somewhere. They grow very fast and spread about 4' in each direction. They are also about 15' tall. They work great but in the winter, they loose all of their leaves so you will not have much of a privacy screen in the winter. Also the more water they get, the faster they grow. If you plant the bareroot trees and water them a lot, they will reach 15' in 2 years.

Bill

Our neighbor planted some hybrid poplars, and they grew extremely fast -- like 15-20 feet in two years. They were bareroot and about 3-4 feet tall when he planted them. I think he got them at Cook's Nursery in Lindon or Orem (can't tell which city it is from the freeway). I'm not sure if they were the same hybrids you're considering, but he said they wouldn't produce the "cotton" that cottonwoods and poplars can make. He ended up pulling them out to build a retaining wall a few years later, so I don't know how tall they would have eventually grown.

If you want some evergreen screen, I keep seeing catalogs mention Thuja 'Green Giant', a form or Arborvitae, which is related to cedars. I just googled it, and the National Arboretum calls it one of their "Elite Plants". It looks very positive. I'm thinking of getting one myself. It is said to grow very fast and like all kinds of soils, from sandy to clay. I didn't see whether it is OK in our alkaline soil or not. Does anyone know that?

I'll put the link below to the U.S. National Arboretum description (PDF file)

Here is a link that might be useful: Green Giant

I was thinking Poplar and arborvitaes also.
The thing with poplars that you will have to take into consideration is do you want to do alot of raking in autumn?
Also, you need to keep the suckers trimmed back or it will look very unkept.
Depending on some factors, Arborvitaes might need to be wrapped during winter to keep them from being damaged from snow weighing down branches from their normal upright position.
The weighting down can either misshape them, of kill the branch leading to dead brown areas or if pruned out... large gaps.

Arborvitaes also can get infestations of spiders... which depending on how you look at it is either a good thing (new webs can actually look pretty, and catch bugs) or a bad thing(old webs look ugly, creepy)

Birds love to nest in Arborvitaes, which will cut down on spider population (in theory, I had birds and still had spiders!)

I have had both, and I prefer poplars... I do not mind raking... kind of relaxing, (Also a good chore for my kids to do) but my main reason is... I do not like planting under arborvitaes and getting a sticker from them in my finger! They REALLY hurt!