Sweeteners vary greatly and so I advise using the one specified in the recipe (if I have specified one) for the best results. I find xylitol works very similar to sugar in baking, it weighs the same like for like as sugar and it is also a natural sweetener.
Xylitol when eaten in large amounts may, like many sweeteners cause a laxative type effect, but I find it is not as bad as other sweeteners in this respect at all. The type of xylitol I purchase is called Total Sweet and is available in many larger supermarkets, health food stores like Holland & Barrett and on Amazon. You can check where your nearest stockist is via this link.
If you choose to use a different sweetener you may need significantly less than the recipe stipulates and you may experience a bitter aftertaste in your desserts.
Xylitol weighs the same like for like as sugar, where as many other sweeteners only need a tiny amount for the same sweetness.
Please note that xylitol is toxic for dogs!