I helped out on a local 'Green team' task yesterday coppicing hazel to open up a main ride through a wood to allow more sunlight to reach the ground and allow certain species of plant to grow to benefit the Silver-Washed Fritillary butterfly.
I came away exhausted but with 4 fine Hazel logs all about 6' long ranging from 2 1/2" to 4 1/2" diameter.
Using an axe and wedges I've split these, one split straight, two split with about 45 degrees of twist and the biggest and what I hoped to be the best split had almost 90 degrees of twist along it's length.
The twist is probably manageable on all of them, and at least I can see it and try to lay out the bow to minimise it.
So the advantage of splitting is you can see any twist, however there is the risk of the split running off to one side and wasting wood so it's a matter of risk management. With easily attainable Hazel I'll split it, but with hard to acquire Yew I'll saw it in the knowledge that I'll discover any twist when I start using hand tools and the Yew (especially a longbow cross section, I think) is more tolerant of twist.
For those of you looking to acquire wood your local conservation group is probably a good source. In the UK you can probably find local groups via your council website or the BTCV (British Trust for Conservation Volunteers).
There are several groups run in my area and they have a program of tasks for the year, so you can pick out the coppicing tasks.
You can see in the pic some of the staves are quite thin and skinny, these will do for experimental 'bend through the handle' American Indian style bows or for tillering demonstrations or kids bows. It's just good to have the staves, I've sealed the end (other brands of PVA are also available !) Once the pva is dry I'll write the date and 'Hazel' on them and get them stacked on my shelves,