I like bigger tubing but tight bends become harder with the much thicker tubing. Smaller tubing kinks a bit more but with a bit of planning, you can get the tightest bends from it and you never have any space issues when using the smaller fittings on some of the trickier blocks like universal GPU blocks.
TBH pick whichever looks best and once it is in your hands, getting it to go where you want to is a synch! If you eventually use a universal block, a few g 1/4 inch male to female adapters would solve any problems if you cant fit your fittings onto the block..