I’ve been tying on tubes for only a few months but here is my input.
The metal tubes that are pre-lined (Kaufman’s sells them) are really nice but too pricey in my opinion.
The metal tubes you can get at hobby shops are nice and priced right and come in smaller diameters (< 1/8” O.D) but you will need to treat the ends so that they do not fray your leader. Steelhead strikes are too far and few between for me to risk loosing one because of a frayed leader. The hobby shops also sell mini tuber cutters ($5) that are just like the ones used for plumbing but for small diameter tubes. I have stopped using this tubing because of the leader issue. Some have had success treating the ends with their Dremel tools.
Metal tubing is also helping in creating a heavier tube fly if getting you fly down is desirable.
As for plastic tubing, in the 1/8” O.D. size I use hard black brake tubing (I got a bunch cheap from Kenworth Trucking parts department in Marysville, WA). This tubing is also flexible enough to accept the eye of your hook so you don’t need to add any flexible tubing to as the hook holder.
Flyfishusa.com (Welches fly shop) sells and inexpensive kit of hard plastic tubes (~$3 for a dozen 6” tubes. These kits come with enough flexible tubing in the correct size for hook holders. The hard tubing is in 1/8” O.D, and also 3/32” O.D. which has become my preferred tube size.