I prefer boots not just for the potentially muddy conditions, but for the additional ankle support, I'm just not used to doing 40k steps a day on uneven terrain (I live in east anglia, we don't have hills here) so I find I'm less susceptible to injury in a boot. I am careful to pick ones that aren't too heavy though, as others have said they can be hard work, especially with half a ton of sticky mud clinging to them! Insoles are handy, good socks and compeed are essential!