While the colour range of the WH is small (only 6 colours) and the yardage is slightly less than the Rowan, it is fairly easily available here and is very reasonably priced.(ASC on the left, WH on the right)
Here are the general specs:
Yardage: ASC - 90m; WH 85m
Composition: ASC: 60% cotton, 40% acrylic; WH - exactly the same
Washing instructions: ASC: warm (40C) machine wash on wool cycle; WH: gentle machine wash
Gauge/tension: ASC: 4.5 - 5.5mm (7-9 US) gives 16-18 st and 23-25 rows over 10cm/4"; WH: 4.5mm (7 US) gives 19 st and 25 rows over 10cm/4".
Origin: ASC - not clear on some ball bands, others say Italy; WH - China.
Price: ASC retails for about $13 in Australia, WH for about $4-5.
Most importantly, how do they feel and compare when knitted? I've used both, and for the same pattern - the monogram cushions I've made for my nephews and nieces (ASC here and WH here).
I think the ASC feels slightly softer in the ball, but the yarn itself looks almost indistinguishable. However, the colours themselves, to me, make the yarns different - the ASC dyes are deeper and more even, the WH is (as the name suggests) slightly washed out and the WH shades are, in side by side comparison, slightly garish tones. This is far less obvious when the WH yarn is viewed by itself.(ASC on the left, WH on the right)
As for the knitted fabric, it is, to me, indistinguishable. Using 4.5mm sticks gives a firm-ish fabric, which is what you want for the cushions. I've knit ASC on 5mm sticks too (for the Trellis toddler cardi) and it gives more drape, but holds the cables well. I'm sure the WH would be the same - the monogram letters on the cushions have really nice stitch definition.
Something to watch with the WH (and from recollection, with the ASC as well) is that the ends tend to untwist. The yarn is made up of a whole bunch of smaller plies, which are themselves plied, and if you leave the ends to darn in once you've finished knitting the whole piece, the yarn will untwist. Easy to fix by a small knot right near the end of the yarn which you just cut off before darning in!
If you can live with the limited colours, then the WH is a great substitue for ASC. Hopefully if we buy lots of it, Patons will increase the colour range (please, pretty please?!).