The pre-made sticks of tubing are neat, but are seldom long enough to do something very long without splices or unions, which might not be desireable for various reasons. In the Standard Parts section of the older Chrysler parts books, there is a part number for bulk steel tubing in various sizes (similar with GM also), but you'll have to do appropriate flaring at each end with appropriate nuts too.
If splices are acceptable, then they could be added to an existing set of lines instead of doing the whole thing over again.
Tubing is inexpensive, but it can be tedious to get the right radius of bend and get it oriented in the correct direction as most turns are compound (the basic curve and then angled at another angle from the base line) as in a fuel line between the carb and fuel pump, for example. Not much fun when you get toward the end and then you end up kinking something! Been there, done that on fuel pump to fuel filter lines, much less a set of trans cooler lines.
Just depends on your level of expertise and availability of spare time. I, personally, had rather be rummaging around a salvage yard than spending an afternoon trying to bend up a set of lines--unless that was the last resort.
Back to the Home of the Forward Look Network