Revivalist said:
Just to throw in an extra opinion . . .
I personally really like using a reservoir for the following reasons (of course, I'm open to correction, just please be coureous. 
) . . .
1. Bleeding the system is easier. The reservoir does it automatically. You can just fill the system and it will essentially bleed itself as all the air eventually gets to the reservoir and goes to the top. A fillport requires that you wait for the bleeding to be done before you close the loop.
Why? The T-line holds extra fluid. It can potentially hold allot more fluid that your particular reservoir if the T is at the bottom of your case and the fill port is at the top of a 22.5 inch case using 1/2" ID tubing.
Revivalist said:
2. Bleeding the system is more thorough. I have noticed that it can take up to 3 days for the bleeding to be absolutely complete. This is evident when all the bubbles have disappeared and the water level in the reservoir drops slightly as the trapped air in the tubes makes its way to the reservoir and up to the top. The reservoir can then be opened and more water added. With a T-line, where does trapped air go after days of use?
In a T-Line setup the idea is to have the bubbles go up as they normally do except instead of floating to the top of a turbulent pool of water, the float to the top of a tube of water. The volume of air that escapes is replaced by an equal volume of water from the T line. A T line can also be refilled.
Revivalist said:
3. It’s easier to prime the pump. With a reservoir, you can just fill it up and add a little more water as necessary when the pump pulls water into the tubes. With a T-line you have to balance a funnel and fill it a little at a time (depending on how big the funnel is). If the pump pulls all the water too quickly, you need to turn it off until you fill the funnel some more since you don’t want to run the pump dry.
I honestly don't see how the process is really any different.
Revivalist said:
4. A reservoir is basically the same price as a T-line. A nice reservoir like the Swiftech MCRES-MICRO is about $15. A “T” and a fill port are about $12+$2 = $14 at Danger Den.
5. A reservoir hardly takes more room than a T-line.
Sure.
Revivalist said:
6. There is more water in the loop for better cooling. More water is able to absorb more heat and emit more heat than less water. A reservoir allows there to be more water (without more tubing which of course would mean more restriction).
The first part of this statement is not well thought out. Depending on the size of the reservoir a T line could have just as much water as a small rez. The second part is flat out wrong. A T line using tubing laid out like this "
┴" with the main water flow going through the bottom of the inverted T. The extra tubing at the top is not a part of the normal flow of water and thus does not add more drag; the water is not flowing through the extra tubing at the top.
Revivalist said:
7. It's easier to see the water level of the system at any time. With time, some amount of water evaporates through the tubes and the water level drops. This can be seen easily with a reservoir. With a T-line, you have to inspect all the tubes for air pockets.
I would argue that unless you're using opaque tubing its easier to see the water level with a T line. You just see how much air/ water is in the vertical bit of tubing. You talk about air pockets in the tubes when water levels drop? Why would there be? The Air bubbles would go the top of the T line just as they would in a reservoir and be replaced by extra fluid. The only time air bubbles would be introduced is if the water levels dropped so far that all the extra fluid was used. The exact same thing would happen using a reservoir if the fluid levels dropped so low.
Revivalist said:
8. A reservoir looks cool, especially with UV reactive coolant. (At least in my opinion. Example: pic1, pic2)
Personal preference.
After deconstructing your post it seems to me that you think a T line is an inverted T ( ┴ ) with some kind of valve where the — and the | meet, thus not allowing air bubbles to escape or extra fluid into the loop to replace the air. This is not the case. The T is just an open junction typically placed a few inches before the intake on the pump. The flow is coming in on the return and any air bubbles in the liquid simply float up to the top of the T.
Look here
And just consider I took the time to go through all this and I’m using a milk jug as a
RESIVOUR.
