I'm using stash for mine - a combination of John Arbon alpaca/merino 4ply, some Blacker classic and some Titus. Here's my swatch.
The Rowan CAL has also given me the confidence to cast on for Marie Wallin's Aster. This is the very first crochet garment I've attempted so am a bit nervous but I do love this deep aubergine colour. I'm not taking any chances with this and am using the yarn called for in the pattern - Rowan's Summerlite 4ply. And it's lovely to work with. I think the sleeves and seaming will be a bit tricky on this, but so far the body seems straightforward and it's quite fun to work on.