I've bought a couple of long sleeve NikePro tops recently, and have a good chance to test them out on a couple of cold nights (temperatures heading towards freezing) and on a milder night. I think they are excellent - on the cold nights, they prevented the cold shock when you first start, but once I got going and started sweating, then I did not get too hot (which has been a problem for me in the past). I guess the fact that there is NO room under the top to trap any warm air also regulates the heat.
On the coldest night on my top half I just wore the NikePro, a cotton t shirt, and a lightweight running jacket (bought from Aldi recently), and temperature wise it was fine. On the warmer night I did not bother with the jacket, and, again, it was all quite comfortable. I'm also pretty sure that "runners nipple" would be a thing of the past wearing these !!!
One thing to be aware of is that once you stop running (I do a walking cool-down) you very quickly lose heat, and can feel chilly in no time. However this seems to be a minor disadvantage in comparison to the benefits.
I wear the Nike Pro range while running, and I quite like them. Have to say though, they are more suited in the winter rather than in the summer, even if Nike claims that you can wear them during the summer. If you wanna wear one underneath, I recommend a sleeveless compression type. I wore one with short sleeves and I overheated a bit.
If you wanna buy one, it would not be a bad thing though because it also has a strange phychological effect on you to carry on. I don't know, maybe it's just me but it's one of the reasons why I regularly wear them.
Now I have not used the Nike Base Layers Compression or Pro but I have used and swear by the HH Dry Base layers. These were the originals and were even made in Olive so squaddies and booties didnt get rollocked for wearing them under kit. Its wicks away the sweat so you dont get cold on cold nights and in warmer conditions does the same but again kicks away the sweat so your more comfortable. I have the long sleeved version as I use it for skiing and rock climbing and running but I was consider the short sleeved version. As for the cheaper base layers I would stay away. The Nike baselayers look really good and I checked them out this weekend. Although I looked at the addidas base layers and on the box it babbled on about its psychological effects and I just laughed and left them on the shelf.
Every sports make under the sun is brining out their "own" version now so dont get ripped off with the hype.
Go with what works and I can assure you the original Helly Hansen layers are spot on. They also do HH Warm which is a pro wool like material.