Absolutely buy what looks appealing to you, what do you want to look at sitting on your desk, table ect for years to come. High split rates on Koa and Redwood don't particularly surprise me as they are faster growing than the other hardwoods you used, more open grain, more chance for flaws defects and voids, shame though the Koa looked so nice after it was turned.
If you have been watching the thread for the last few days you will know I am one of the 1-2% (mines cherry) that had a nano split, and can personally vouch for how painless it was to get it fixed. Granted the entire process would take longer for most of you that don't live less than an hour from epic, because of shipping, but as stated in a previous post they removed and replaced the shell (wood part), and got it shipped back out the same day they received it from me.
The other great thing is if you don't see something that catches your eye or want something really special Andy gives you the option to send in your own wood for the nano to be made of. In the near future I hope to add a custom or two to my collection. I have some Brazilian Rosewood I've had forever and a couple other rare pieces that were ment for pool cue inlays and what not that I need to do something with so it doesn't just sit forever, you can't import it anymore and its just to good looking to sit the woodshop for much longer. Unfortunately my back prevents me from doing all but the most basic of projects anymore so new uses need to be found for all the pretty wood I've been hoarding,
@Snappo has provided people with some gorgeous pieces of various burls if that's your thing, and if it is hit him up you won't be disappointed.
TL;DR: get what you think looks best, maybe even a custom send in your own wood version. It's hand made from wood it might crack or split (that's why the warranty is so awesome thanks Andy) but the process to get it fixed is fast easy and painless (no idea for the process for customs that may split) got mine back in just a few days.