My favorite would have to be T.s.parietalis(Red Sided garter snake)..........Just kidding. They are a great snake but as for me it's........
T.radix(Plains garter snake),
just like having an old dog. They get comfortable and seem to look forward to constant interaction.
I've seen behavior that borders on intelligence. I love all the garter snakes I keep but mark me down as a radix fanatic