Some people have had problems with pumps and controllers with 6mm hose and others haven't. You will find that the varistream controllers and shurflo pumps are not warrantied for use with either 6mm or 8mm hose.
8mm hose is going to put less strain on you pump as the water can flow more freely. I tend to average about 2-3 years from a Flojet pump using 6mm hose and no flow controller just a shut off valve on the pole.
Any of the options can work well, if possible have a try of someone else's set-up to see what works for them.