I prefer playing 10 minutes with changes, offsides decided by the home team. Having line changes adds an extra tactical and strategic aspect to the game; when to change, what line to put on, how to balance the lines etc. It also makes time outs mean something (more) because you can replenish energy that way. Its also fun using the lesser known players, its also an all round more inclusive, more complete use of the game imo.
If you're playing 5 minute period line changes are a little more pointless, because one shift could take half the period.