I use the 3/8" tubing from Midwest (#6910) with my autosiphon for racking. I use some 5/16" from the local hardware store for blowoff tubes, since it's easier to push into my drilled stoppers than the 3/8" is. I'd go larger, if I was using fruit or something that might plug 5/16".
It's all vinyl. There may be lead in the stuff from the hardware store, but it never really contacts the beer I drink, so I don't worry.
I just got some Watts SVIG20 3/8" from Amazon for cheap to use for racking. It is supposedly safe up to 170F.
I like to replace my tubing pretty often - whenever it becomes discolored. Unnecessary, but inexpensive.