I've tried both and they are both good but something in me just can't square cooking with cola, i'm not a massive fan of spreading sugar or treacle on gammon either so that's probably part of it. I use Mary Berry's recipe with cider, i'll be using it on Boxing day when I cook for 14. You can carve it when it's done.
I'm doing the Nigella one in the slow cooker with red wine and spices. I'm another one who can't quite bring myself to cooke with Coke (even though I drink it), I also don't like too much sweetness in savoury meals.
I've done gammon in coke and and in cider in the past. Yesterday I was pushed for time and bought a bog standard large gammon joint from Morrisons and simply simmered it for 3 hours on the hob in ordinary water and then turned off the heat and let it cool overnight in the pan. We ate some today and it was absolutely lovely. It tasted of good, old fashioned ham and nothing else