In terms of difference between them, broadly – the Max is a ‘mountain bike’ the Pace is a ‘racer’, so your choice depends on your style of paddling and expected use. 

The Max is a slightly more stable board- therefore a little less manoeuvrable than the Pace. The Max has a 130kg Max recommended payload, the Pace 120kg, so the Max has the edge for touring or carrying small passengers. 

The Pace offers a little more fun as you develop skills – slightly more manoeuvrable and quicker but a shade more balance required. 

You may find it more rewarding once you progress past the novice phase. Having said that, they are both aimed at novices and either board will certainly give you lots of rewarding paddling.