Assuming your talking about your crankcase, go with the thicker oil. 10w30 is to lightweight for the abuse it will take. I would get crankcase specific oil, i run 85w
The 75w-80 trans oil is not thicker than the 10w-30 in this case due to it is not gear oil. The 75w gear oil is much thicker. We have been a believer in the Honda trans oil in their red bottle. Almost any oil will work as long as it doesn't have friction inhibitors in it.