Type of ethernet cable for skybox f3

hi i have the skybox f3 and use wi fi dongle,find it bit glitchy and think its the dongle as have heard good reviews bout my server ,i was looking to get an ethernet cable and run it from router and was wondering does it matter what ethernet cable i purchase as i see category 5e and category 6 ethernet cables on ebay,will need a long ethernet cable,would prefer using ethernet cable than homeplugs ,any advice would be appreciated,would post links but my post count isnt high enough
cheers