I would recommend braid main line with a braid leader myself. Firstly, by having a thicker braid leader you will stand less chance of cracking-off which can easily happen when casting the heavy weight of a spod. Secondly, it will increase the life of your braid because the leader will take all the hard work. Occasionally the leader may need changing, whereas the braid beneath should remain pretty fresh. Leader-wise I use 50lb Arma-Kord which is extremely durable.
One common mistake I see with anglers spodding tackle is the thickness of the cheap braid they use; often resembling granny’s wool. I use either Daiwa Tournament Braid and Berkley Whiplash in 30lb that are both extremely thin and excellent and with a little looking after they should last years. The reason the thicker braids aren’t so good, is not only are they prone to wind knots, but they catch the wind reducing the accuracy of the cast. Remember: when loading your braid, it’s best to leave a lip at the top of spool, as this will reduce the risk of potentially very costly braid wind knots.
As for attaching them together, I use a knot I believe is called the Mahin. It starts by making an Overhand Knot in the leader without tightening it down. The main line braid is then passed through the back of the knot and wrapped up around the leader 10 times, then six times back down the leader before exiting the Overhand Knot in the SAME DIRECTION as it went in (very important). Then simply moisten before tighten. If using heavier braid, the number of turns may need reducing. This knots tags both exit towards the reel making it very streamlined. Happy spodding, get on the munga!