Strawbale is going to have a higher r value. Straw is going to have r-30 or r-2.25 per inch.
http://www.greenhomebuilding.com/QandA/strawbale/misc.htm "The R-Value of a bale wall assembly is approximately R-30. This is the resistivity number. The inverse would be the conductivity or 1/30 = 0.0333."
Light straw is going to have a lower r value at r-18 or r 1.5 per inch. This is because a LSC wall should not be greater than 12" thick or else it may rot.
http://www.greenhomebuilding.com/QandA/cob/strawclay.htm "Depending on how much clay you add and how much you compress it, you could expect an R-value of around 1.5 to 2 per inch of thickness for a light straw clay wall. That compares to almost R-4 per inch of thickness for fiberglass. So you will need twice the thickness of straw-clay as you would fiberglass to reach the same nominal R-value. In fact, however, the straw-clay wall will perform better than would be predicted from this equation, both because of the added thermal mass effect and because the straw-clay fills the cavity more completely than fiberglass batting."
These links and quotes are from Michael Smith's Q/A on greenhomebuilding.com.
You could also get similar information in this book
https://www.amazon.com/Essential-Light-Straw-Construction-Step/dp/0865718431/ref=sr_1_1?ie=UTF8&qid=1535052685&sr=8-1&keywords=light+straw+clay which I highly recommend as it has case studies done.
