Agree - none is the answer. Runner beans like a good, rich, preferably trenched by digging deep and filling with good compost and soil to make a deep and fertile root run. You might be able to grow dwarf french type beans, not sure, they certainly can be grown in pots.

I agree too, runner beans won't so in a Growbag!

I agree with the other responders: None. A growbag simply isn't deep enough.

However if you get one of those big plastic containers meant for potatoes you can get four runner beans in.