THe powerstream is the most powerful and highest quality PSU there.
The Enermax Noisetaker is right behind it and is a very nice PSU as well.
The Modstream doesn't have as much power as either of these but the fact that it is modular as well as sporting a 120mm fan is a defenite plus. Still pretty powerful though.
The other Enermax is more entry level powersupply. THe regular enermax PSUs are tested at 25C something a normal PSU would never experience, the Noisetakers are tested at 40C much more realistic. I would expect it to be decent but not worth the money.
THe Ultra, there is a lot of controversy here. The Ultra has all the rails feeding off of one line which puts a lot of strain on that one cable. However the ENTIRE PSU is modular and has a sleek finish which is nice. OTOH the inside is not nice, it has very small heatsinks and capacitors, and the fans are not very high quality. Also although under a light load it is solid, if you were to put it near its peak load it craps out. I believe one reviewer uses lgihtbulbs to test PSU's. He has like 8 bulbs and lights one and tests then lights another and tests etc. The Ultra crapped out at #3 where it would only post at 4 they couldn't even do that.
-Kevin