I use 7ft of 3/16 I was under the impression that 1/4 isnt suppossed to be used because it will cause tons of foaming. 3/16’s is much more of a pain in the ass to get onto the 1/4 barbed fittings.
1/4" is just too big for the lengths we typically run. If your keg is less than 20’ from your tap, you need 3/16", otherwise you’ll be pouring a glass of foam. If you’re worried about having more than 1 line diameter, just make them all 3/16", gas doesn’t mind.